ICSE – Grade 9 – Chemistry – Ch 05 – QA

Questions & Answers

ICSE - Grade - 9

Subject: Chemistry

Chapter - 05 - The Periodic Table

Types of Questions

MCQ

  1. Who first attempted to classify elements into groups of three called triads?
     a) Mendeleev
     b) Newlands
     c) Dobereiner
     d) Moseley
     Answer: c) Dobereiner


  2. In Dobereiner’s triad, the atomic mass of the middle element was approximately the ________ of the other two.
     a) Product
     b) Average
     c) Difference
     d) Sum
     Answer: b) Average


  3. Which of the following is an example of Dobereiner’s triad?
     a) Li, Na, K
     b) Ca, Sr, Ba
     c) F, Cl, Br
     d) All of these
     Answer: d) All of these


  4. Newlands’ classification was called the law of ________.
     a) Triads
     b) Octaves
     c) Periodicity
     d) Atomic numbers
     Answer: b) Octaves


  5. According to Newlands, every ________ element had properties similar to the first.
     a) Fifth
     b) Sixth
     c) Seventh
     d) Eighth
     Answer: d) Eighth


  6. Who is credited with the development of the modern periodic law?
     a) Mendeleev
     b) Moseley
     c) Newlands
     d) Dobereiner
     Answer: b) Moseley


  7. The modern periodic law is based on the ________ of elements.
     a) Atomic mass
     b) Valency
     c) Atomic number
     d) Density
     Answer: c) Atomic number


  8. Who first arranged elements in order of increasing atomic mass in a systematic table?
     a) Mendeleev
     b) Newlands
     c) Lavoisier
     d) Dalton
     Answer: a) Mendeleev


  9. Mendeleev left ________ in his periodic table for undiscovered elements.
     a) No gaps
     b) Random elements
     c) Vacant spaces
     d) Extra columns
     Answer: c) Vacant spaces


  10. Eka-aluminium predicted by Mendeleev was later discovered as ________.
     a) Gallium
     b) Germanium
     c) Scandium
     d) Aluminium
     Answer: a) Gallium


  11. Eka-silicon was later discovered as ________.
     a) Silicon
     b) Gallium
     c) Germanium
     d) Indium
     Answer: c) Germanium


  12. Mendeleev’s periodic law stated that the properties of elements are a periodic function of their ________.
     a) Atomic numbers
     b) Atomic masses
     c) Electronic configurations
     d) Valencies
     Answer: b) Atomic masses


  13. Which pair of elements showed an anomaly in Mendeleev’s table?
     a) Na and K
     b) Ar and K
     c) Te and I
     d) Cl and F
     Answer: c) Te and I


  14. The position of isotopes could not be explained in Mendeleev’s table because they had different ________.
     a) Atomic numbers
     b) Atomic masses
     c) Valencies
     d) Shells
     Answer: b) Atomic masses


  15. In the modern periodic table, isotopes are placed in the same position because they have the same ________.
     a) Mass number
     b) Atomic number
     c) Valency
     d) Density
     Answer: b) Atomic number


  16. How many groups are present in the modern periodic table?
     a) 7
     b) 8
     c) 18
     d) 9
     Answer: c) 18


  17. How many periods are present in the modern periodic table?
     a) 6
     b) 7
     c) 8
     d) 9
     Answer: b) 7


  18. The elements in a group have the same number of ________.
     a) Shells
     b) Neutrons
     c) Valence electrons
     d) Protons
     Answer: c) Valence electrons


  19. The elements in a period have the same number of ________.
     a) Protons
     b) Neutrons
     c) Shells
     d) Valence electrons
     Answer: c) Shells


  20. Which element’s position is still uncertain in the modern periodic table?
     a) Hydrogen
     b) Helium
     c) Neon
     d) Argon
     Answer: a) Hydrogen


  21. Group 1 elements are called ________.
     a) Alkaline earth metals
     b) Alkali metals
     c) Transition metals
     d) Noble gases
     Answer: b) Alkali metals


  22. Group 2 elements are called ________.
     a) Alkali metals
     b) Halogens
     c) Alkaline earth metals
     d) Noble gases
     Answer: c) Alkaline earth metals


  23. Group 17 elements are called ________.
     a) Halogens
     b) Noble gases
     c) Transition elements
     d) Metalloids
     Answer: a) Halogens


  24. Group 18 elements are called ________.
     a) Halogens
     b) Noble gases
     c) Transition metals
     d) Inner transition elements
     Answer: b) Noble gases


  25. Which group elements are known as representative elements?
     a) Groups 1, 2 and 13–18
     b) Groups 3–12
     c) Only Group 1
     d) Only Group 18
     Answer: a) Groups 1, 2 and 13–18


  26. Which block elements are transition metals?
     a) s-block
     b) p-block
     c) d-block
     d) f-block
     Answer: c) d-block


  27. Inner transition elements are placed in the ________ block.
     a) s-block
     b) p-block
     c) d-block
     d) f-block
     Answer: d) f-block


  28. Lanthanoids and actinoids are examples of ________.
     a) Transition elements
     b) Noble gases
     c) Inner transition elements
     d) Representative elements
     Answer: c) Inner transition elements


  29. Which group elements are monoatomic and inert?
     a) Group 1
     b) Group 2
     c) Group 17
     d) Group 18
     Answer: d) Group 18


  30. The metallic character ________ down a group.
     a) Increases
     b) Decreases
     c) Remains constant
     d) Becomes zero
     Answer: a) Increases


  31. The metallic character ________ across a period.
     a) Increases
     b) Decreases
     c) Remains same
     d) Fluctuates
     Answer: b) Decreases


  32. Atomic size increases as we move ________.
     a) Across a period
     b) Down a group
     c) Diagonally
     d) Randomly
     Answer: b) Down a group


  33. Atomic size decreases as we move ________.
     a) Across a period (left to right)
     b) Down a group
     c) Randomly
     d) In transition series
     Answer: a) Across a period (left to right)


  34. The oxides of metals are generally ________.
     a) Basic
     b) Acidic
     c) Neutral
     d) Amphoteric
     Answer: a) Basic


  35. The oxides of non-metals are generally ________.
     a) Basic
     b) Acidic
     c) Neutral
     d) Amphoteric
     Answer: b) Acidic


  36. Which alkali metal reacts vigorously with water?
     a) Sodium
     b) Potassium
     c) Lithium
     d) All of these
     Answer: d) All of these


  37. The action of water on alkali metals forms ________.
     a) Hydroxides and oxygen
     b) Hydroxides and hydrogen
     c) Oxides and hydrogen
     d) Oxides and water
     Answer: b) Hydroxides and hydrogen


  38. Alkaline earth metals have ________ valence electrons.
     a) 1
     b) 2
     c) 3
     d) 4
     Answer: b) 2


  39. Which alkaline earth metal does not react with water?
     a) Beryllium
     b) Calcium
     c) Strontium
     d) Barium
     Answer: a) Beryllium


  40. The halogens have ________ valence electrons.
     a) 5
     b) 6
     c) 7
     d) 8
     Answer: c) 7


  41. The most reactive halogen is ________.
     a) Fluorine
     b) Chlorine
     c) Bromine
     d) Iodine
     Answer: a) Fluorine


  42. The least reactive halogen is ________.
     a) Fluorine
     b) Chlorine
     c) Bromine
     d) Iodine
     Answer: d) Iodine


  43. Noble gases have ________ valency.
     a) 0
     b) 1
     c) 2
     d) Variable
     Answer: a) 0


  44. Noble gases exist as ________.
     a) Monoatomic gases
     b) Diatomic molecules
     c) Polyatomic molecules
     d) Solids
     Answer: a) Monoatomic gases


  45. Which noble gas is used in balloons and cryogenics?
     a) Helium
     b) Neon
     c) Argon
     d) Krypton
     Answer: a) Helium


  46. Which noble gas is used in advertising signs?
     a) Helium
     b) Neon
     c) Argon
     d) Xenon
     Answer: b) Neon


  47. Which noble gas is used in electric bulbs to provide an inert atmosphere?
     a) Helium
     b) Neon
     c) Argon
     d) Xenon
     Answer: c) Argon


  48. Mendeleev predicted eka-aluminium to have properties similar to ________.
     a) Aluminium
     b) Silicon
     c) Gallium
     d) Germanium
     Answer: a) Aluminium


  49. The gradual change in properties of elements across a period or down a group is called ________.
     a) Periodicity
     b) Triads
     c) Octaves
     d) Classification
     Answer: a) Periodicity


  50. Which scientist proved that atomic number is more fundamental than atomic mass?
     a) Mendeleev
     b) Moseley
     c) Newlands
     d) Dobereiner
     Answer: b) Moseley

Fill in the Blanks

  1. The elements are classified to study their properties in a ______ manner.
     Answer: systematic


  2. Dobereiner grouped elements into sets of three known as ______.
     Answer: triads


  3. In Dobereiner’s triads, the atomic mass of the middle element was approximately the ______ of the other two.
     Answer: mean


  4. Dobereiner’s triads could not include all the elements known at that time, so the law was ______.
     Answer: discarded


  5. Newlands arranged elements in the order of increasing ______.
     Answer: atomic mass


  6. Newlands’ classification is known as the law of ______.
     Answer: octaves


  7. According to Newlands, every ______ element had properties similar to the first.
     Answer: eighth


  8. Newlands’ law worked well only up to the element ______.
     Answer: calcium


  9. Newlands was honoured in the year ______ for his contribution to classification.
     Answer: 1887


  10. Mendeleev arranged elements in the increasing order of their ______.
     Answer: atomic masses


  11. Mendeleev stated that the properties of elements are a periodic function of their ______.
     Answer: atomic masses


  12. Mendeleev’s table left ______ for undiscovered elements.
     Answer: gaps


  13. Mendeleev successfully predicted the properties of undiscovered elements such as ______.
     Answer: eka-aluminium


  14. Mendeleev corrected the wrong ______ of some elements.
     Answer: atomic masses


  15. A major defect of Mendeleev’s table was the anomalous pair of ______ and ______.
     Answer: cobalt, nickel


  16. Isotopes could not be placed properly in Mendeleev’s table because they have different ______ but the same chemical properties.
     Answer: atomic masses


  17. In Mendeleev’s table, chemically dissimilar elements were grouped together, for example, copper and ______.
     Answer: silver


  18. Mendeleev’s table also separated chemically similar elements, such as gold and ______.
     Answer: platinum


  19. The arrangement of elements in the modern periodic table is based on their ______.
     Answer: atomic numbers


  20. The modern periodic law was given by ______.
     Answer: Moseley


  21. The modern periodic law states that the properties of elements are a periodic function of their ______.
     Answer: atomic numbers


  22. The position of isotopes was explained in the modern periodic table because they have the same ______.
     Answer: atomic number


  23. The anomaly of potassium and argon was resolved in the modern periodic table due to their different ______.
     Answer: atomic numbers


  24. In the modern periodic table, elements with similar properties are placed in vertical columns called ______.
     Answer: groups


  25. The horizontal rows in the modern periodic table are called ______.
     Answer: periods


  26. Groups indicate the number of ______ electrons in an element.
     Answer: valence


  27. Periods indicate the number of ______ in an element.
     Answer: shells


  28. The representative elements belong to the groups ______ to ______.
     Answer: 1, 7


  29. The transition elements belong to groups ______ to ______.
     Answer: 3, 12


  30. Inner transition elements include the ______ and ______ series.
     Answer: lanthanide, actinide


  31. The noble gases are placed in group ______.
     Answer: 18


  32. Noble gases are also known as ______ gases.
     Answer: inert


  33. The atomic size ______ as we go down a group.
     Answer: increases


  34. The atomic size ______ as we move across a period from left to right.
     Answer: decreases


  35. Metallic character ______ down a group.
     Answer: increases


  36. Metallic character ______ across a period from left to right.
     Answer: decreases


  37. Valency remains the same down a group but ______ across a period.
     Answer: changes


  38. The elements of group I are called ______ metals.
     Answer: alkali


  39. The alkali metals react vigorously with ______ to form hydroxides.
     Answer: water


  40. The alkali metals are stored under ______ to prevent reaction with air and moisture.
     Answer: kerosene


  41. Group II elements are called ______ earth metals.
     Answer: alkaline


  42. Alkaline earth metals also form ______ when they react with water.
     Answer: hydroxides


  43. Group 17 elements are known as the ______.
     Answer: halogens


  44. Halogens form ______ bonds with metals.
     Answer: ionic


  45. Group 18 elements exist in the form of ______ atoms.
     Answer: monoatomic


  46. Argon is used in electric bulbs because it is ______.
     Answer: inert


  47. Neon is used in ______ signs.
     Answer: advertising


  48. The noble gases have complete ______ shells.
     Answer: outer


  49. Oxides of metals are generally ______ in nature.
     Answer: basic


  50. Oxides of non-metals are generally ______ in nature.
     Answer: acidic

Name the Following

  1. The scientist who gave the law of triads.
     Answer: Dobereiner


  2. The set of three elements with similar properties arranged in increasing atomic mass.
     Answer: Triad


  3. The scientist who gave the law of octaves.
     Answer: Newlands


  4. The year in which Newlands was honoured for his work.
     Answer: 1887


  5. The scientist who gave the first widely accepted periodic table.
     Answer: Mendeleev


  6. The law proposed by Mendeleev regarding periodicity.
     Answer: Mendeleev’s Periodic Law


  7. The element predicted by Mendeleev as eka-aluminium.
     Answer: Gallium


  8. The element predicted by Mendeleev as eka-boron.
     Answer: Scandium


  9. The element predicted by Mendeleev as eka-silicon.
     Answer: Germanium


  10. The scientist who suggested atomic number as the basis of classification.
     Answer: Moseley


  11. The law given by Moseley.
     Answer: Modern Periodic Law


  12. The table based on increasing atomic number.
     Answer: Modern Periodic Table


  13. The vertical columns of the modern periodic table.
     Answer: Groups


  14. The horizontal rows of the modern periodic table.
     Answer: Periods


  15. Elements belonging to groups 1 and 2 and 13 to 17.
     Answer: Representative elements


  16. Elements of groups 3 to 12.
     Answer: Transition elements


  17. Elements of the lanthanide series.
     Answer: Inner transition elements


  18. Elements of the actinide series.
     Answer: Inner transition elements


  19. Elements of group 18.
     Answer: Noble gases (or Inert gases)


  20. The group of elements also called halogens.
     Answer: Group 17


  21. The group of elements also called alkali metals.
     Answer: Group 1


  22. The group of elements also called alkaline earth metals.
     Answer: Group 2


  23. The gas used in electric bulbs because of its inertness.
     Answer: Argon


  24. The noble gas used in advertising signboards.
     Answer: Neon


  25. The noble gas used in weather balloons.
     Answer: Helium


  26. The noble gas used in filling high voltage lamps.
     Answer: Xenon


  27. The noble gas used in fluorescent tubes and sodium lamps.
     Answer: Krypton


  28. The noble gas used in cryogenics and as a coolant.
     Answer: Helium


  29. The noble gas used in the treatment of cancer.
     Answer: Radon


  30. The elements which show variable valency and form coloured compounds.
     Answer: Transition elements


  31. The series of 14 elements after lanthanum.
     Answer: Lanthanides


  32. The series of 14 elements after actinium.
     Answer: Actinides


  33. The group in which hydrogen is placed in the modern periodic table.
     Answer: Group 1 (alkali metals)


  34. The group in which hydrogen also shows similarity with non-metals.
     Answer: Group 17 (halogens)


  35. The elements whose oxides are basic in nature.
     Answer: Metals


  36. The elements whose oxides are acidic in nature.
     Answer: Non-metals


  37. The elements whose oxides are amphoteric in nature.
     Answer: Aluminium and Zinc


  38. The element which forms the lightest alkali metal.
     Answer: Lithium


  39. The element which forms the heaviest alkali metal.
     Answer: Francium


  40. The element used in fireworks and signal flares among alkaline earth metals.
     Answer: Magnesium


  41. The element in alkaline earth metals used in building material like cement.
     Answer: Calcium


  42. The halogen used as a disinfectant in water.
     Answer: Chlorine


  43. The halogen used in the manufacture of antiseptics and medicines.
     Answer: Iodine


  44. The halogen used in non-stick cookware coatings.
     Answer: Fluorine


  45. The halogen used in photography.
     Answer: Bromine


  46. The element having atomic number 3.
     Answer: Lithium


  47. The element having atomic number 11.
     Answer: Sodium


  48. The element having atomic number 19.
     Answer: Potassium


  49. The element having atomic number 20.
     Answer: Calcium


  50. The inert gas having atomic number 10.
     Answer: Neon

Answer in One Word

  1. Who proposed the law of triads?
     Answer: Dobereiner


  2. Who gave the law of octaves?
     Answer: Newlands


  3. Who gave the first widely accepted periodic table?
     Answer: Mendeleev


  4. Who gave the modern periodic law?
     Answer: Moseley


  5. Which property forms the basis of Mendeleev’s periodic table?
     Answer: Atomic mass


  6. Which property forms the basis of the modern periodic table?
     Answer: Atomic number


  7. What are the vertical columns in the periodic table called?
     Answer: Groups


  8. What are the horizontal rows in the periodic table called?
     Answer: Periods


  9. What is the group name of alkali metals?
     Answer: Group 1


  10. What is the group name of alkaline earth metals?
     Answer: Group 2


  11. What is the group name of halogens?
     Answer: Group 17


  12. What is the group name of noble gases?
     Answer: Group 18


  13. What is the other name for noble gases?
     Answer: Inert gases


  14. What is the lightest alkali metal?
     Answer: Lithium


  15. What is the heaviest alkali metal?
     Answer: Francium


  16. Which alkali metal is used in street lighting?
     Answer: Sodium


  17. Which alkaline earth metal is used in fireworks?
     Answer: Magnesium


  18. Which alkaline earth metal is used in cement and mortar?
     Answer: Calcium


  19. Which halogen is used as a disinfectant in water?
     Answer: Chlorine


  20. Which halogen is used in antiseptics and medicines?
     Answer: Iodine


  21. Which halogen is used in non-stick cookware coatings?
     Answer: Fluorine


  22. Which halogen is used in photography?
     Answer: Bromine


  23. Which noble gas is used in electric bulbs?
     Answer: Argon


  24. Which noble gas is used in advertising signboards?
     Answer: Neon


  25. Which noble gas is used in weather balloons?
     Answer: Helium


  26. Which noble gas is used in cancer treatment?
     Answer: Radon


  27. Which noble gas is used in fluorescent tubes?
     Answer: Krypton


  28. Which noble gas is used in high-voltage lamps?
     Answer: Xenon


  29. Which series contains lanthanides?
     Answer: Inner transition


  30. Which series contains actinides?
     Answer: Inner transition


  31. Which element was predicted as eka-aluminium?
     Answer: Gallium


  32. Which element was predicted as eka-boron?
     Answer: Scandium


  33. Which element was predicted as eka-silicon?
     Answer: Germanium


  34. Which element shows similarity with alkali metals and halogens?
     Answer: Hydrogen


  35. Which oxides are basic in nature?
     Answer: Metals


  36. Which oxides are acidic in nature?
     Answer: Non-metals


  37. Which oxides are amphoteric in nature?
     Answer: Aluminium


  38. Which property increases down a group?
     Answer: Atomic size


  39. Which property decreases across a period?
     Answer: Atomic size


  40. Which property increases across a period?
     Answer: Non-metallic character


  41. Which property increases down a group?
     Answer: Metallic character


  42. Which particle decides the atomic number of an element?
     Answer: Proton


  43. Which shell indicates the period number?
     Answer: Outer shell


  44. Which type of elements show variable valency and coloured compounds?
     Answer: Transition elements


  45. Which type of elements are monoatomic in nature?
     Answer: Noble gases


  46. Which group elements form salts called halides?
     Answer: Halogens


  47. Which group elements are stored under kerosene oil?
     Answer: Alkali metals


  48. Which element is used in signal flares?
     Answer: Magnesium


  49. Which element is used in photographic plates?
     Answer: Silver bromide


  50. Which element’s position was explained correctly by modern periodic law instead of Mendeleev’s?
     Answer: Argon

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Find the Odd Man Out

  1. Lithium, Sodium, Potassium, Chlorine
     Answer: Chlorine
     Explanation: Others are alkali metals, while chlorine is a halogen.


  2. Magnesium, Calcium, Barium, Fluorine
     Answer: Fluorine
     Explanation: Others are alkaline earth metals, while fluorine is a halogen.


  3. Fluorine, Chlorine, Bromine, Oxygen
     Answer: Oxygen
     Explanation: Others are halogens, while oxygen is a chalcogen.


  4. Helium, Neon, Argon, Sodium
     Answer: Sodium
     Explanation: Others are noble gases, while sodium is an alkali metal.


  5. Scandium, Titanium, Iron, Oxygen
     Answer: Oxygen
     Explanation: Others are transition metals, while oxygen is a non-metal.


  6. Gallium, Germanium, Scandium, Helium
     Answer: Helium
     Explanation: Others were predicted by Mendeleev, while helium is a noble gas.


  7. Hydrogen, Lithium, Sodium, Potassium
     Answer: Hydrogen
     Explanation: Others are alkali metals, hydrogen is a non-metal.


  8. Lithium, Sodium, Potassium, Calcium
     Answer: Calcium
     Explanation: Others are group 1 elements, calcium belongs to group 2.


  9. Beryllium, Magnesium, Calcium, Sodium
     Answer: Sodium
     Explanation: Others are alkaline earth metals, sodium is an alkali metal.


  10. Neon, Argon, Krypton, Bromine
     Answer: Bromine
     Explanation: Others are noble gases, bromine is a halogen.


  11. Chlorine, Bromine, Iodine, Argon
     Answer: Argon
     Explanation: Others are halogens, argon is a noble gas.


  12. Sodium, Magnesium, Potassium, Rubidium
     Answer: Magnesium
     Explanation: Others are alkali metals, magnesium is an alkaline earth metal.


  13. Cobalt, Nickel, Iron, Hydrogen
     Answer: Hydrogen
     Explanation: Others are transition metals, hydrogen is a non-metal.


  14. Radon, Krypton, Helium, Calcium
     Answer: Calcium
     Explanation: Others are noble gases, calcium is an alkaline earth metal.


  15. Aluminium, Zinc, Iron, Copper
     Answer: Aluminium
     Explanation: Others are transition metals, aluminium is not.


  16. Lithium, Sodium, Potassium, Zinc
     Answer: Zinc
     Explanation: Others are alkali metals, zinc is a transition metal.


  17. Fluorine, Chlorine, Bromine, Sulphur
     Answer: Sulphur
     Explanation: Others are halogens, sulphur is a chalcogen.


  18. Helium, Neon, Argon, Fluorine
     Answer: Fluorine
     Explanation: Others are noble gases, fluorine is a halogen.


  19. Sodium, Potassium, Cesium, Magnesium
     Answer: Magnesium
     Explanation: Others are alkali metals, magnesium is an alkaline earth metal.


  20. Chlorine, Bromine, Iodine, Oxygen
     Answer: Oxygen
     Explanation: Others are halogens, oxygen is a chalcogen.


  21. Hydrogen, Oxygen, Fluorine, Chlorine
     Answer: Hydrogen
     Explanation: Others form diatomic halogen molecules, hydrogen is not a halogen.


  22. Iron, Copper, Silver, Neon
     Answer: Neon
     Explanation: Others are metals, neon is a noble gas.


  23. Lithium, Sodium, Potassium, Argon
     Answer: Argon
     Explanation: Others are alkali metals, argon is a noble gas.


  24. Magnesium, Calcium, Strontium, Chlorine
     Answer: Chlorine
     Explanation: Others are alkaline earth metals, chlorine is a halogen.


  25. Helium, Neon, Argon, Sodium
     Answer: Sodium
     Explanation: Others are noble gases, sodium is an alkali metal.


  26. Chlorine, Bromine, Iodine, Helium
     Answer: Helium
     Explanation: Others are halogens, helium is a noble gas.


  27. Scandium, Titanium, Vanadium, Oxygen
     Answer: Oxygen
     Explanation: Others are transition metals, oxygen is a non-metal.


  28. Gallium, Germanium, Eka-aluminium, Calcium
     Answer: Calcium
     Explanation: Others are predicted/discovered through Mendeleev’s periodic table, calcium is not.


  29. Potassium, Rubidium, Caesium, Iron
     Answer: Iron
     Explanation: Others are alkali metals, iron is a transition metal.


  30. Beryllium, Magnesium, Calcium, Iodine
     Answer: Iodine
     Explanation: Others are alkaline earth metals, iodine is a halogen.


  31. Hydrogen, Lithium, Sodium, Rubidium
     Answer: Hydrogen
     Explanation: Others are true alkali metals, hydrogen is not.


  32. Copper, Silver, Gold, Oxygen
     Answer: Oxygen
     Explanation: Others are coinage metals, oxygen is a non-metal.


  33. Neon, Argon, Krypton, Radon
     Answer: Radon
     Explanation: Others are lighter noble gases, radon is radioactive.


  34. Fluorine, Chlorine, Bromine, Neon
     Answer: Neon
     Explanation: Others are halogens, neon is a noble gas.


  35. Scandium, Titanium, Chromium, Sodium
     Answer: Sodium
     Explanation: Others are transition metals, sodium is an alkali metal.


  36. Helium, Neon, Argon, Hydrogen
     Answer: Hydrogen
     Explanation: Others are noble gases, hydrogen is not.


  37. Sodium, Potassium, Cesium, Calcium
     Answer: Calcium
     Explanation: Others are group 1 elements, calcium is group 2.


  38. Chlorine, Bromine, Iodine, Sulphur
     Answer: Sulphur
     Explanation: Others are halogens, sulphur is not.


  39. Iron, Cobalt, Nickel, Gallium
     Answer: Gallium
     Explanation: Others are transition metals, gallium is not.


  40. Helium, Neon, Argon, Lithium
     Answer: Lithium
     Explanation: Others are noble gases, lithium is an alkali metal.


  41. Magnesium, Calcium, Barium, Sodium
     Answer: Sodium
     Explanation: Others are alkaline earth metals, sodium is an alkali metal.


  42. Chlorine, Bromine, Iodine, Helium
     Answer: Helium
     Explanation: Others are halogens, helium is a noble gas.


  43. Copper, Silver, Gold, Platinum
     Answer: Platinum
     Explanation: Others are coinage metals, platinum is not.


  44. Lithium, Sodium, Potassium, Magnesium
     Answer: Magnesium
     Explanation: Others are alkali metals, magnesium is an alkaline earth metal.


  45. Helium, Neon, Argon, Oxygen
     Answer: Oxygen
     Explanation: Others are noble gases, oxygen is not.


  46. Fluorine, Chlorine, Bromine, Argon
     Answer: Argon
     Explanation: Others are halogens, argon is a noble gas.


  47. Sodium, Potassium, Rubidium, Copper
     Answer: Copper
     Explanation: Others are alkali metals, copper is a transition metal.


  48. Magnesium, Calcium, Strontium, Chlorine
     Answer: Chlorine
     Explanation: Others are alkaline earth metals, chlorine is a halogen.


  49. Neon, Krypton, Argon, Sodium
     Answer: Sodium
     Explanation: Others are noble gases, sodium is an alkali metal.


  50. Fluorine, Chlorine, Iodine, Nitrogen
     Answer: Nitrogen
     Explanation: Others are halogens, nitrogen is not.

Match the Pair

Set 1

Match the following:

Column A

  1. Dobereiner
  2. Newland
  3. Mendeleev
  4. Moseley
  5. Noble gases

Column B
 a. Arranged elements by atomic number
 b. Introduced triads
 c. Discovered later but fitted well in modern table
 d. Law of Octaves
 e. Left gaps for undiscovered elements

Answers:
 1 – b
 2 – d
 3 – e
 4 – a
 5 – c

Set 2

Match the following:

Column A

  1. Eka-silicon
  2. Group I
  3. Group II
  4. Group 17
  5. Group 18

Column B
 a. Halogens
 b. Alkali metals
 c. Germanium
 d. Noble gases
 e. Alkaline earth metals

Answers:
 1 – c
 2 – b
 3 – e
 4 – a
 5 – d

Set 3

Match the following:

Column A

  1. Germanium
  2. Chlorine
  3. Helium
  4. Calcium
  5. Sodium

Column B
 a. Alkali metal
 b. Eka-silicon predicted by Mendeleev
 c. Noble gas used in balloons
 d. Alkaline earth metal
 e. Halogen

Answers:
 1 – b
 2 – e
 3 – c
 4 – d
 5 – a

Set 4

Match the following:

Column A

  1. Periodicity
  2. Transition metals
  3. Inert gases
  4. Fluorine
  5. Argon

Column B
 a. First noble gas discovered
 b. Repetition of properties at regular intervals
 c. Most reactive halogen
 d. Coloured compounds
 e. Stable outermost shell

Answers:
 1 – b
 2 – d
 3 – e
 4 – c
 5 – a

Set 5

Match the following:

Column A

  1. Oxides of non-metals
  2. Oxides of alkali metals
  3. Group 1 metals
  4. Group 2 metals
  5. Group 17 elements

Column B
 a. Acidic
 b. Basic
 c. Divalent
 d. Univalent
 e. Salt formers

Answers:
 1 – a
 2 – b
 3 – d
 4 – c
 5 – e

Set 6

Match the following:

Column A

  1. John Newland
  2. Dmitri Mendeleev
  3. Henry Moseley
  4. Dobereiner
  5. Hydrogen

Column B
 a. Triads
 b. Dual position (alkali metals and halogens)
 c. Law of Octaves
 d. Modern periodic law
 e. Left gaps

Answers:
 1 – c
 2 – e
 3 – d
 4 – a
 5 – b

Set 7

Match the following:

Column A

  1. Group
  2. Period
  3. Atomic size down a group
  4. Atomic size across a period
  5. Metallic character across a period

Column B
 a. Decreases
 b. Same number of shells
 c. Decreases
 d. Same number of valence electrons
 e. Increases

Answers:
 1 – d
 2 – b
 3 – e
 4 – a
 5 – c

Set 8

Match the following:

Column A

  1. Alkali metals
  2. Alkaline earth metals
  3. Transition elements
  4. Inner transition elements
  5. Noble gases

Column B
 a. Lanthanides and actinides
 b. Group 1
 c. Group 18
 d. Groups 3 to 12
 e. Group 2

Answers:
 1 – b
 2 – e
 3 – d
 4 – a
 5 – c

Set 9

Match the following:

Column A

  1. Sodium in water
  2. Calcium in water
  3. Chlorine in water
  4. Helium
  5. Neon

Column B
 a. Displaces hydrogen slowly
 b. Kills germs in drinking water
 c. Used in advertising signs
 d. Explosive reaction, forms hydroxide
 e. Used in balloons

Answers:
 1 – d
 2 – a
 3 – b
 4 – e
 5 – c

Set 10

Match the following:

Column A

  1. Argon and potassium anomaly
  2. Isotopes
  3. Eka-boron
  4. Fluorine
  5. Krypton

Column B
 a. Problem due to same chemical properties but different masses
 b. Placement justified by atomic number
 c. Most electronegative element
 d. Noble gas
 e. Predicted element (later discovered as scandium)

Answers:
 1 – b
 2 – a
 3 – e
 4 – c
 5 – d

Short Answer Questions  

  1. Q: What is a triad in Dobereiner’s classification?
     A: A group of three elements with the middle element’s atomic mass being the average of the other two.


  2. Q: Why was Dobereiner’s triad law discarded?
     A: It could not include all known elements.


  3. Q: What did Newland observe in his Law of Octaves?
     A: Properties of elements repeated after every eighth element.


  4. Q: Why was Newland’s law of octaves discarded?
     A: It failed for elements beyond calcium.


  5. Q: Who predicted eka-silicon?
     A: Mendeleev.


  6. Q: What is the significance of the gaps in Mendeleev’s table?
     A: They indicated undiscovered elements.


  7. Q: Why were isotopes a problem in Mendeleev’s classification?
     A: They have different atomic masses but same chemical properties.


  8. Q: What does modern periodic law state?
     A: Properties of elements are a periodic function of their atomic numbers.


  9. Q: Who arranged elements in order of increasing atomic number?
     A: Moseley.


  10. Q: What is periodicity?
     A: The repetition of properties at regular intervals.


  11. Q: How do elements in the same group compare chemically?
     A: They have similar chemical properties.


  12. Q: How do elements in the same period compare in shell structure?
     A: They have the same number of shells.


  13. Q: Why does atomic size decrease across a period?
     A: Increasing nuclear charge pulls electrons closer to the nucleus.


  14. Q: Why does atomic size increase down a group?
     A: New electron shells are added.


  15. Q: How does metallic character vary across a period?
     A: It decreases across a period.


  16. Q: How does metallic character vary down a group?
     A: It increases down a group.


  17. Q: Which group has one valence electron?
     A: Group 1 (alkali metals).


  18. Q: Which group has two valence electrons?
     A: Group 2 (alkaline earth metals).


  19. Q: Why are alkali metals highly reactive?
     A: They easily lose their single valence electron.


  20. Q: Why are alkaline earth metals less reactive than alkali metals?
     A: They have two valence electrons and stronger metallic bonding.


  21. Q: What are transition metals known for?
     A: Forming coloured compounds and variable valency.


  22. Q: What are inner transition elements?
     A: Lanthanides and actinides placed separately at the bottom of the periodic table.


  23. Q: Why are noble gases inert?
     A: They have complete outermost electron shells.


  24. Q: What are halogens?
     A: Group 17 elements that form salts with metals.


  25. Q: Why do halogens exist as diatomic molecules?
     A: Each atom needs one electron to complete its octet.


  26. Q: What is the electronic configuration of Group 1 elements?
     A: ns¹.


  27. Q: What is the electronic configuration of Group 2 elements?
     A: ns².


  28. Q: What is the valency of halogens?
     A: One.


  29. Q: How does valency vary across a period?
     A: It increases from 1 to 8.


  30. Q: What type of oxides do non-metals form?
     A: Acidic oxides.


  31. Q: What type of oxides do alkali metals form?
     A: Basic oxides.


  32. Q: What happens when sodium reacts with water?
     A: It forms sodium hydroxide and hydrogen.


  33. Q: What happens when calcium reacts with water?
     A: It forms calcium hydroxide and hydrogen slowly.


  34. Q: Why does reactivity of alkali metals increase down the group?
     A: Atomic size increases and valence electron is lost more easily.


  35. Q: Why does reactivity of halogens decrease down the group?
     A: Atomic size increases and attraction for electron decreases.


  36. Q: What is the main feature of Mendeleev’s periodic table?
     A: Elements arranged by increasing atomic mass with similar properties in same group.


  37. Q: How was the anomaly of argon and potassium resolved?
     A: By arranging elements according to atomic number.


  38. Q: Why is hydrogen placed separately in the periodic table?
     A: It resembles both alkali metals and halogens.


  39. Q: What is the group number of noble gases?
     A: Group 18.


  40. Q: Which element is used in balloons due to low density and non-flammability?
     A: Helium.


  41. Q: Which noble gas is used in advertising signs?
     A: Neon.


  42. Q: Why are transition metals good conductors?
     A: They have free d-electrons.


  43. Q: What is the atomic number of an element?
     A: Number of protons in its nucleus.


  44. Q: Why does metallic character increase down a group?
     A: Valence electrons are farther from the nucleus and lost more easily.


  45. Q: Why does non-metallic character decrease down a group?
     A: Attraction for electrons decreases.


  46. Q: What is the difference between a period and a group?
     A: Periods are horizontal rows; groups are vertical columns.


  47. Q: What is the general trend of atomic size in periods?
     A: Decreases from left to right.


  48. Q: What is the general trend of atomic size in groups?
     A: Increases down the group.


  49. Q: Why are Group 2 oxides less basic than Group 1 oxides?
     A: Alkaline earth metals are less reactive than alkali metals.


  50. Q: Name an element predicted by Mendeleev that was later discovered.
     A: Germanium (eka-silicon).

Puzzles

  1. Q: I am a Group 1 element, very soft and highly reactive, used in street lamps. Who am I?
     A: Sodium


  2. Q: I am an inert gas used in balloons. Who am I?
     A: Helium


  3. Q: I am predicted by Mendeleev as eka-silicon. Who am I?
     A: Germanium


  4. Q: I am a halogen that disinfects water. Who am I?
     A: Chlorine


  5. Q: I am a Group 2 metal, harder than sodium, react slowly with water. Who am I?
     A: Calcium


  6. Q: I am a noble gas used in neon lights. Who am I?
     A: Neon


  7. Q: I am the first element of the periodic table. Who am I?
     A: Hydrogen


  8. Q: I am a triad element between calcium and barium. Who am I?
     A: Strontium


  9. Q: I am an alkali metal that reacts violently with water to form hydrogen. Who am I?
     A: Potassium


  10. Q: I am a halogen in Group 17 with the highest reactivity. Who am I?
     A: Fluorine


  11. Q: I am a metal oxide that is strongly basic. Who am I?
     A: Sodium oxide


  12. Q: I am a non-metal oxide that is acidic. Who am I?
     A: Carbon dioxide


  13. Q: I am a transition metal that forms coloured compounds. Who am I?
     A: Copper


  14. Q: I belong to period 2 and have two valence electrons. Who am I?
     A: Beryllium


  15. Q: I am an element in Group 18 with complete outer shell, used in lasers. Who am I?
     A: Neon


  16. Q: I am a Group 1 metal, soft, and react with oxygen to form peroxides. Who am I?
     A: Potassium


  17. Q: I am a halogen with a diatomic molecule and used in disinfectants. Who am I?
     A: Chlorine


  18. Q: I am a Group 2 element, form alkaline solutions with water. Who am I?
     A: Magnesium


  19. Q: I am a halogen that is dark brown and volatile. Who am I?
     A: Bromine


  20. Q: I am a noble gas with atomic number 36. Who am I?
     A: Krypton


  21. Q: I am an element whose isotopes caused issues in Mendeleev’s classification. Who am I?
     A: Chlorine


  22. Q: I am the metal in Mendeleev’s triad with lithium and potassium. Who am I?
     A: Sodium


  23. Q: I am a Group 17 element used in antiseptics. Who am I?
     A: Iodine


  24. Q: I am a transition element used in jewellery due to lustre. Who am I?
     A: Gold


  25. Q: I am a Group 18 element that is completely inert and monoatomic. Who am I?
     A: Argon


  26. Q: I am a soft, highly reactive alkali metal stored under oil. Who am I?
     A: Sodium


  27. Q: I am a halogen less reactive than chlorine. Who am I?
     A: Bromine


  28. Q: I am an element with electronic configuration 1s² 2s² 2p⁶. Who am I?
     A: Neon


  29. Q: I am a metal forming strong hydroxide with water and belong to Group 2. Who am I?
     A: Calcium


  30. Q: I am a halogen that combines with sodium to form common salt. Who am I?
     A: Chlorine


  31. Q: I am a Group 1 metal used in making soaps. Who am I?
     A: Sodium


  32. Q: I am an element that completes period 2 in the periodic table. Who am I?
     A: Neon


  33. Q: I am a Group 2 element used in fireworks to give red colour. Who am I?
     A: Strontium


  34. Q: I am a noble gas heavier than neon but lighter than xenon. Who am I?
     A: Argon


  35. Q: I am an element that forms coloured compounds and variable valency. Who am I?
     A: Iron


  36. Q: I am the first element in the halogen group. Who am I?
     A: Fluorine


  37. Q: I am a period 3 element with metallic character. Who am I?
     A: Sodium


  38. Q: I am a noble gas with very low reactivity used in light bulbs. Who am I?
     A: Argon


  39. Q: I am a Group 1 element in Mendeleev’s triad with lithium and potassium. Who am I?
     A: Sodium


  40. Q: I am a halogen element with atomic number 53. Who am I?
     A: Iodine


  41. Q: I am a transition metal often used as a catalyst. Who am I?
     A: Platinum


  42. Q: I am a noble gas used in cryogenics. Who am I?
     A: Helium


  43. Q: I am a Group 2 element that forms a protective oxide layer. Who am I?
     A: Magnesium


  44. Q: I am a halogen element with greenish-yellow gas. Who am I?
     A: Chlorine


  45. Q: I am an alkali metal that floats on water. Who am I?
     A: Sodium


  46. Q: I am a transition metal forming blue solutions. Who am I?
     A: Copper


  47. Q: I am a noble gas used in lasers. Who am I?
     A: Neon


  48. Q: I am a Group 17 element used in iodized salt. Who am I?
     A: Iodine


  49. Q: I am a halogen less reactive than fluorine but more reactive than iodine. Who am I?
     A: Chlorine


  50. Q: I am an element whose atomic number determines its position in modern periodic table. Who am I?
     A: Any element (general concept – atomic number basis)

Difference Between:

  1. Q: Difference between Alkali Metals and Alkaline Earth Metals
     A:
  • Alkali Metals (Group 1): Soft, highly reactive metals with one valence electron; react violently with water to form hydroxides and hydrogen.
  • Alkaline Earth Metals (Group 2): Harder, less reactive metals with two valence electrons; react slowly with water to form hydroxides and hydrogen.



  1. Q: Difference between Halogens and Noble Gases
    A:
  • Halogens (Group 17): Reactive non-metals with seven valence electrons; exist as diatomic molecules; form salts with metals.
  • Noble Gases (Group 18): Chemically inert gases with complete outer shells; monoatomic; rarely form compounds.



  1. Q: Difference between Mendeleev’s Periodic Table and Modern Periodic Table
    A:
  • Mendeleev: Elements arranged by atomic mass; left gaps for undiscovered elements; some anomalies in order of properties.
  • Modern Table: Elements arranged by atomic number; periodicity of properties maintained; anomalies resolved (e.g., argon-potassium).



  1. Q: Difference between Periods and Groups
    A:
  • Periods: Horizontal rows; elements have same number of electron shells; properties change gradually across a period.
  • Groups: Vertical columns; elements have same number of valence electrons; show similar chemical properties.



  1. Q: Difference between Representative Elements and Transition Elements
    A:
  • Representative Elements: Belong to s- and p-block; show regular periodic properties; variable valency usually limited.
  • Transition Elements: Belong to d-block; partially filled d-orbitals; show variable oxidation states and coloured compounds.



  1. Q: Difference between Inner Transition Elements and Transition Elements
    A:
  • Inner Transition Elements: f-block elements; lanthanides and actinides; filling of f-orbitals; similar properties within series.
  • Transition Elements: d-block elements; filling of d-orbitals; coloured compounds; variable valency.



  1. Q: Difference between Metallic Oxides and Non-metallic Oxides
    A:
  • Metallic Oxides: Formed by metals; usually basic; react with water to form hydroxides.
  • Non-metallic Oxides: Formed by non-metals; usually acidic; react with water to form acids.



  1. Q: Difference between Atomic Mass and Atomic Number
    A:
  • Atomic Mass: Mass of an atom in atomic mass units (u); includes protons and neutrons; not strictly periodic.
  • Atomic Number: Number of protons in nucleus; determines chemical properties; basis of modern periodic table.



  1. Q: Difference between Alkali Metals and Hydrogen
    A:
  • Alkali Metals: Soft metals, highly reactive, metallic in nature; form oxides and hydroxides.
  • Hydrogen: Non-metal, forms covalent compounds, can act like alkali metals or halogens; diatomic gas.



  1. Q: Difference between Electropositive and Electronegative Elements
    A:
  • Electropositive: Metals; tendency to lose electrons to form positive ions.
  • Electronegative: Non-metals; tendency to gain electrons to form negative ions.



  1. Q: Difference between Atomic Size Across a Period and Down a Group
    A:
  • Across a Period: Atomic size decreases due to increasing nuclear charge pulling electrons closer.
  • Down a Group: Atomic size increases due to addition of electron shells.



  1. Q: Difference between Metallic Character Across a Period and Down a Group
    A:
  • Across a Period: Metallic character decreases; elements become more non-metallic.
  • Down a Group: Metallic character increases; elements become more reactive metals.



  1. Q: Difference between Reactivity of Alkali Metals and Halogens
    A:
  • Alkali Metals: Reactivity increases down the group due to larger atomic size; easier to lose valence electron.
  • Halogens: Reactivity decreases down the group due to larger atomic size; harder to gain an electron.



  1. Q: Difference between Mendeleev’s Gaps and Modern Table Arrangement
    A:
  • Mendeleev’s Gaps: Left empty spaces for undiscovered elements; predicted properties.
  • Modern Table: No gaps; elements arranged strictly by atomic number; anomalies resolved.



  1. Q: Difference between Softness of Alkali Metals and Hardness of Alkaline Earth Metals
    A:
  • Alkali Metals: Soft due to weak metallic bonds (one valence electron).
  • Alkaline Earth Metals: Harder due to stronger metallic bonds (two valence electrons).



  1. Q: Difference between Chemical Properties of Group 1 and Group 2 Elements
    A:
  • Group 1: Highly reactive; form strong bases; react violently with water.
  • Group 2: Less reactive; form weaker bases; react slowly with water.



  1. Q: Difference between Periodicity in Mendeleev’s Table and Modern Table
    A:
  • Mendeleev: Periodicity observed in properties with atomic mass; some anomalies.
  • Modern: Periodicity observed with atomic number; all anomalies resolved.



  1. Q: Difference between Atomic Structure of Alkali Metals and Halogens
    A:
  • Alkali Metals: One electron in outermost shell; easily lost; forms cations.
  • Halogens: Seven electrons in outermost shell; easily gain one electron; forms anions.



  1. Q: Difference between Oxides of Group 1 and Group 2 Metals
    A:
  • Group 1 Oxides: Strongly basic; react vigorously with water.
  • Group 2 Oxides: Less basic; react slowly with water.



  1. Q: Difference between Lanthanides and Actinides
    A:
  • Lanthanides: 4f orbitals filled; metallic; similar chemical properties; used in phosphors and alloys.
  • Actinides: 5f orbitals filled; mostly radioactive; used in nuclear fuel and weapons.

Assertion and Reason

  1.  

Assertion (A): Dobereiner grouped elements into triads.
 Reason (R): In each triad, the atomic mass of the middle element was the average of the other two.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Dobereiner’s Triads law could not be applied to all known elements.
 Reason (R): Many elements did not fit into triads.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Newland arranged elements in order of increasing atomic masses.
 Reason (R): He observed repetition of properties at every 8th element.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Newland’s Law of Octaves was discarded.
 Reason (R): It could not accommodate elements discovered later.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Newland was honoured by the Royal Society in 1887.
 Reason (R): He was the first to show periodicity of properties in elements.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Mendeleev arranged elements in increasing atomic number.
 Reason (R): Atomic number was not known in Mendeleev’s time.


 Answer: A is false, R is true.

  1.  

Assertion (A): Mendeleev left gaps in his periodic table.
 Reason (R): He predicted existence of undiscovered elements.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Mendeleev predicted properties of germanium before its discovery.
 Reason (R): He named it eka-silicon.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Mendeleev corrected the atomic mass of beryllium.
 Reason (R): He used periodic properties to justify placement.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Isotopes posed a problem in Mendeleev’s table.
 Reason (R): They have different atomic masses but same chemical properties.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Argon was placed before potassium in the modern periodic table.
 Reason (R): Atomic number, not atomic mass, is the basis of classification.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Modern periodic law is based on atomic number.
 Reason (R): Atomic number represents nuclear charge.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Elements in a group have similar chemical properties.
 Reason (R): They have the same number of valence electrons.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Elements in a period have the same number of shells.
 Reason (R): The principal quantum number is the same for all elements in a period.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Metallic character decreases across a period.
 Reason (R): Effective nuclear charge increases across a period.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Atomic size increases down a group.
 Reason (R): New shells are added down the group.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Atomic size decreases across a period.
 Reason (R): Nuclear charge increases while new shells are not added.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Alkali metals are highly reactive.
 Reason (R): They have one electron in their outermost shell.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Alkali metals readily form positive ions.
 Reason (R): They lose their single valence electron easily.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Alkaline earth metals are divalent.
 Reason (R): They have two valence electrons.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Transition metals are good conductors of heat and electricity.
 Reason (R): They have free electrons.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Transition metals form coloured compounds.
 Reason (R): Presence of unpaired d-electrons allows electronic transitions.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Noble gases are inert.
 Reason (R): They have complete outermost electron shells.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Group 17 elements are called halogens.
 Reason (R): They react with metals to form salts.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Halogens are diatomic.
 Reason (R): Each atom needs one electron to complete its octet.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Hydrogen was difficult to place in Mendeleev’s table.
 Reason (R): It resembles both alkali metals and halogens.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Inner transition elements are placed separately at the bottom of the table.
 Reason (R): This keeps the periodic table compact.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Metallic character increases down a group.
 Reason (R): Valence electrons are lost more easily.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Non-metallic character increases across a period.
 Reason (R): Nuclear charge increases and tendency to gain electrons rises.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Elements in the same group form similar oxides.
 Reason (R): They have the same valency.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Group I oxides are basic in nature.
 Reason (R): Alkali metals readily form hydroxides with water.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Group II oxides are less basic than Group I oxides.
 Reason (R): Alkaline earth metals are less reactive than alkali metals.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Noble gases exist as monoatomic molecules.
 Reason (R): Their outer shells are completely filled.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Valency varies across a period.
 Reason (R): Number of valence electrons changes from 1 to 8.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Elements of Group 18 have zero valency.
 Reason (R): Their outermost shell is stable.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Mendeleev could group chemically similar elements together.
 Reason (R): He gave importance to properties over atomic mass.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Mendeleev’s periodic law is no longer valid.
 Reason (R): Modern periodic law is based on atomic number.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Potassium is more reactive than sodium.
 Reason (R): Potassium has a larger atomic size and loses its valence electron more easily.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Fluorine is the most reactive halogen.
 Reason (R): It has the smallest atomic radius and highest electronegativity.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Periodicity refers to repetition of properties.
 Reason (R): Properties repeat after regular intervals due to similar electronic configurations.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Group 1 metals are soft and can be cut with a knife.
 Reason (R): They have weak metallic bonds due to large atomic size.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Alkali metals react vigorously with water.
 Reason (R): They liberate hydrogen and form hydroxides.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Noble gases are used in advertising signs.
 Reason (R): They emit coloured light when electrically excited.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Helium is used in filling balloons.
 Reason (R): It is lighter than air and non-inflammable.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Chlorine is used in water purification.
 Reason (R): It kills harmful bacteria.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Noble gases form very few compounds.
 Reason (R): They have stable electronic configurations.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Metallic character decreases across a period.
 Reason (R): Increase in nuclear charge holds electrons more tightly.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Non-metals generally form acidic oxides.
 Reason (R): They combine with oxygen to form covalent oxides.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Calcium reacts less vigorously with water than sodium.
 Reason (R): Calcium is an alkaline earth metal with stronger metallic bonding.
 Answer: Both A and R are true, and R is the correct explanation of A.



  1.  

Assertion (A): Group 17 elements are highly electronegative.
 Reason (R): They have seven valence electrons and a strong tendency to gain one electron.
 Answer: Both A and R are true, and R is the correct explanation of A.

True or False

  1. Dobereiner arranged elements in groups of three called triads.
     Answer: True


  2. In Dobereiner’s triads, the atomic mass of the middle element was always the average of the other two.
     Answer: True


  3. Dobereiner’s triads law applied to all known elements.
     Answer: False


  4. Newland’s law of octaves stated that every 8th element had similar properties.
     Answer: True


  5. Newland arranged elements in increasing order of atomic number.
     Answer: False


  6. Newland was honoured by the Royal Society in 1887.
     Answer: True


  7. Newland’s law of octaves failed because it worked only till calcium.
     Answer: True


  8. Mendeleev arranged elements in increasing order of atomic mass.
     Answer: True


  9. Mendeleev left no gaps in his table.
     Answer: False


  10. Mendeleev predicted properties of elements not discovered in his time.
     Answer: True


  11. Eka-silicon predicted by Mendeleev was later discovered as germanium.
     Answer: True


  12. Mendeleev corrected the atomic mass of beryllium.
     Answer: True


  13. Isotopes created difficulty in Mendeleev’s classification.
     Answer: True


  14. In Mendeleev’s table, potassium was placed before argon.
     Answer: False


  15. Modern periodic law is based on atomic number.
     Answer: True


  16. Atomic number represents the number of protons in an atom.
     Answer: True


  17. Periodicity means repetition of properties at regular intervals.
     Answer: True


  18. Elements in the same group have the same number of shells.
     Answer: False


  19. Elements in the same period have the same number of valence electrons.
     Answer: False


  20. Elements in the same group have similar chemical properties.
     Answer: True


  21. Elements in the same period have the same number of shells.
     Answer: True


  22. Atomic size increases across a period.
     Answer: False


  23. Atomic size decreases across a period.
     Answer: True


  24. Atomic size increases down a group.
     Answer: True


  25. Metallic character decreases across a period.
     Answer: True


  26. Metallic character increases down a group.
     Answer: True


  27. Non-metallic character increases across a period.
     Answer: True


  28. Non-metallic character increases down a group.
     Answer: False


  29. Alkali metals are highly reactive.
     Answer: True


  30. Alkali metals have two valence electrons.
     Answer: False


  31. Alkaline earth metals are divalent.
     Answer: True


  32. Transition elements belong to Groups 3 to 12.
     Answer: True


  33. Transition elements form coloured compounds.
     Answer: True


  34. Inner transition elements include lanthanides and actinides.
     Answer: True


  35. Noble gases are inert because they have incomplete outer shells.
     Answer: False


  36. Group 17 elements are called halogens.
     Answer: True


  37. Halogens form salts with metals.
     Answer: True


  38. Fluorine is the least reactive halogen.
     Answer: False


  39. Noble gases are monoatomic in nature.
     Answer: True


  40. Helium is used in balloons because it is inflammable and lighter than air.
     Answer: True


  41. Neon is used in advertising signs.
     Answer: True


  42. Chlorine is used in water purification.
     Answer: True


  43. Metallic oxides are usually acidic.
     Answer: False


  44. Non-metallic oxides are usually acidic.
     Answer: True


  45. Sodium reacts explosively with water to form sodium hydroxide and hydrogen.
     Answer: True


  46. Calcium reacts vigorously with water just like sodium.
     Answer: False


  47. Group 2 oxides are less basic than Group 1 oxides.
     Answer: True


  48. Hydrogen fits perfectly in Mendeleev’s table.
     Answer: False


  49. Noble gases were not discovered when Mendeleev gave his table.
     Answer: True


  50. Argon is heavier than potassium but is placed before it in the modern periodic table.
     Answer: True

Long Answer Questions

  1. Q: Explain Dobereiner’s Triads.
     A: Dobereiner arranged some elements in groups of three called triads, where the middle element’s atomic mass was approximately the average of the other two, and the elements exhibited similar chemical properties. Examples include lithium, sodium, potassium; calcium, strontium, barium.


  2. Q: Why was Dobereiner’s Triads law discarded?
     A: The law could not be applied to all known elements as many elements did not fit into triads. It was limited to a few elements and lacked a general application.


  3. Q: State Newland’s Law of Octaves.
     A: John Newland observed that if elements were arranged in increasing order of atomic mass, the properties of every eighth element repeated, similar to the octaves in music.


  4. Q: What were the merits of Newland’s classification?
     A: It was the first to show periodicity of properties, arranged elements in order of increasing mass, and helped in predicting properties of unknown elements to some extent.


  5. Q: Why was Newland’s law of octaves discarded?
     A: It failed for elements beyond calcium, could not accommodate newly discovered elements, and forced elements with different properties to be placed together.


  6. Q: Who was Mendeleev and what is his periodic law?
     A: Dmitri Mendeleev arranged elements in order of increasing atomic mass and stated that “the properties of elements are a periodic function of their atomic masses.”


  7. Q: What are the essential features of Mendeleev’s periodic table?
     A: Elements were arranged in increasing order of atomic mass; similar elements were placed in the same group; periods were formed when properties repeated; gaps were left for undiscovered elements.


  8. Q: Mention the merits of Mendeleev’s table.
     A: It grouped elements with similar properties, left gaps for undiscovered elements, predicted properties of unknown elements, and corrected atomic masses of some elements based on periodicity.


  9. Q: State the defects of Mendeleev’s table.
     A: Anomalous pairs like Te-I, position of isotopes could not be explained, chemically similar elements were separated, dissimilar elements grouped together, and hydrogen’s placement was uncertain.


  10. Q: How was the anomaly of argon and potassium explained?
     A: By arranging elements according to atomic number instead of atomic mass, argon (Z=18) was placed before potassium (Z=19), correcting Mendeleev’s anomaly.


  11. Q: Explain the modern periodic law.
     A: It states that “the properties of elements are a periodic function of their atomic numbers.” This solved anomalies in Mendeleev’s table and formed the basis of the modern periodic table.


  12. Q: Describe the salient features of the modern periodic table.
     A: Elements are arranged in order of increasing atomic number; vertical columns are called groups; horizontal rows are called periods; chemically similar elements are in the same group; table is divided into s-, p-, d-, and f-blocks.


  13. Q: Define a group in the periodic table.
     A: A vertical column in the periodic table, containing elements with the same number of valence electrons and similar chemical properties.


  14. Q: Define a period in the periodic table.
     A: A horizontal row in the periodic table, where elements have the same number of electron shells but properties vary gradually.


  15. Q: What are representative elements?
     A: Elements of Groups 1, 2, and 13 to 18, having outermost electrons in s- or p-orbitals, exhibiting regular periodic trends, and predictable chemical properties.


  16. Q: Mention main characteristics of representative elements.
     A: Regular variation in properties across periods, predictable valency, formation of compounds typical for their group, and general trends in metallic/non-metallic character.


  17. Q: What are transition elements?
     A: Elements of d-block (Groups 3 to 12) with partially filled d-orbitals, showing variable valency, forming coloured compounds, and acting as good catalysts.


  18. Q: Mention main characteristics of transition elements.
     A: Variable oxidation states, formation of coloured compounds, catalytic activity, and presence of unpaired d-electrons.


  19. Q: What are inner transition elements?
     A: Lanthanides and actinides placed separately at the bottom of the periodic table, having partially filled f-orbitals.


  20. Q: Mention main characteristics of inner transition elements.
     A: Similar properties in each series, variable oxidation states, and elements show gradual change in properties across the series.


  21. Q: What are inert gases?
     A: Group 18 elements with complete outermost electron shells, chemically very stable and mostly unreactive.


  22. Q: Mention merits of the modern periodic table.
     A: Corrects anomalies of Mendeleev’s table, groups chemically similar elements, explains isotopes, and predicts properties based on atomic number.


  23. Q: Mention defects of the modern periodic table.
     A: Some elements of f-block are separated from main table, placement of hydrogen is not perfect, and new elements require careful insertion.


  24. Q: How does valency vary in a group?
     A: It remains generally the same down a group as elements have the same number of valence electrons.


  25. Q: How does valency vary in a period?
     A: It increases from 1 to 4 and then decreases from 4 to 0 across the period.


  26. Q: How does atomic size vary in a group?
     A: It increases down a group due to addition of new electron shells.


  27. Q: How does atomic size vary across a period?
     A: It decreases across a period due to increasing nuclear charge pulling electrons closer.


  28. Q: How does metallic character vary down a group?
     A: It increases as outer electrons are farther from the nucleus and lost more easily.


  29. Q: How does metallic character vary across a period?
     A: It decreases as elements on the right have higher nuclear charge and gain electrons more readily.


  30. Q: Describe properties of Group 1 metals (Alkali metals).
     A: Soft, highly reactive, low melting points, react with air and water to form hydroxides, have one valence electron.


  31. Q: Describe properties of Group 2 metals (Alkaline earth metals).
     A: Harder than Group 1, less reactive, react slowly with water, form oxides and hydroxides, have two valence electrons.


  32. Q: How do alkali metals react with water?
     A: They react vigorously to form metal hydroxides and hydrogen gas.


  33. Q: How do alkaline earth metals react with water?
     A: They react slowly with water to form hydroxides and hydrogen gas.


  34. Q: Describe properties of halogens.
     A: Diatomic non-metals, highly electronegative, form salts with metals, reactivity decreases down the group.


  35. Q: Describe properties of noble gases.
     A: Monoatomic, inert, colourless, tasteless, odourless, have complete outer electron shells.


  36. Q: How are oxides of metals generally classified?
     A: Oxides of metals are usually basic, while oxides of non-metals are acidic.


  37. Q: What is the action of alkali metals with air?
     A: They oxidise rapidly to form metal oxides.


  38. Q: What is the action of alkaline earth metals with air?
     A: They form oxides slowly when heated.


  39. Q: Why does fluorine show maximum reactivity among halogens?
     A: It has the smallest size, high electronegativity, and strong tendency to gain one electron.


  40. Q: Why do noble gases not form compounds easily?
     A: They have complete outer electron shells and are chemically stable.


  41. Q: What is the significance of periodic trends?
     A: Periodic trends help predict physical and chemical properties of elements based on their position in the periodic table.


  42. Q: Why was Mendeleev’s table successful despite some defects?
     A: It grouped elements by properties, left gaps for undiscovered elements, and predicted properties accurately.


  43. Q: How did Moseley correct anomalies in Mendeleev’s table?
     A: By arranging elements according to atomic number instead of atomic mass.


  44. Q: Give an example of an element predicted by Mendeleev.
     A: Germanium (eka-silicon).


  45. Q: What is the electronic configuration of alkali metals?
     A: ns¹, where n is the period number.


  46. Q: What is the electronic configuration of alkaline earth metals?
     A: ns², where n is the period number.


  47. Q: How does reactivity of alkali metals vary down the group?
     A: Reactivity increases due to increasing atomic size and weaker attraction of valence electron.


  48. Q: How does reactivity of halogens vary down the group?
     A: Reactivity decreases as atomic size increases and attraction for electrons reduces.


  49. Q: How are inner transition elements arranged?
     A: They are placed separately at the bottom of the periodic table in two rows: lanthanides and actinides.


  50. Q: Mention the uses of the periodic table.
     A: It helps predict properties, reactivity, valency, and existence of undiscovered elements, and explains chemical behaviour systematically.

Give Reasons

  1. Q: Give reason why Dobereiner’s triads could not include all elements.
     A: Many elements did not fit into triads, so the law was limited.


  2. Q: Give reason why Newland’s law of octaves was discarded.
     A: It failed beyond calcium and forced dissimilar elements together.


  3. Q: Give reason why Mendeleev left gaps in his periodic table.
     A: To accommodate undiscovered elements with predicted properties.


  4. Q: Give reason why isotopes posed a problem in Mendeleev’s classification.
     A: They have different atomic masses but same chemical properties.


  5. Q: Give reason why modern periodic law is based on atomic number.
     A: Arranging by atomic number resolves anomalies like argon-potassium.


  6. Q: Give reason why elements in the same group have similar chemical properties.
     A: They have the same number of valence electrons.


  7. Q: Give reason why atomic size decreases across a period.
     A: Increasing nuclear charge pulls electrons closer to the nucleus.


  8. Q: Give reason why atomic size increases down a group.
     A: New electron shells are added, increasing size.


  9. Q: Give reason why metallic character decreases across a period.
     A: Non-metals on the right gain electrons instead of losing them.


  10. Q: Give reason why metallic character increases down a group.
     A: Valence electrons are farther from the nucleus and easily lost.


  11. Q: Give reason why alkali metals are highly reactive.
     A: They have one valence electron which is easily lost.


  12. Q: Give reason why reactivity of alkali metals increases down the group.
     A: Atomic size increases, making it easier to lose valence electron.


  13. Q: Give reason why reactivity of halogens decreases down the group.
     A: Atomic size increases, reducing electron affinity.


  14. Q: Give reason why halogens exist as diatomic molecules.
     A: Each atom needs one electron to complete its octet.


  15. Q: Give reason why noble gases are chemically inert.
     A: They have complete outer electron shells.


  16. Q: Give reason why transition metals form coloured compounds.
     A: They have partially filled d-orbitals that absorb visible light.


  17. Q: Give reason why transition elements show variable oxidation states.
     A: They have similar energy d- and s-orbitals allowing multiple valencies.


  18. Q: Give reason why inner transition elements are placed separately.
     A: Their f-orbitals are being filled and properties are similar within series.


  19. Q: Give reason why hydrogen is placed separately in the periodic table.
     A: It resembles both alkali metals and halogens but fits fully in neither.


  20. Q: Give reason why calcium reacts slowly with water.
     A: Its valence electrons are held more tightly than sodium, making reaction slower.


  21. Q: Give reason why sodium reacts violently with water.
     A: Sodium loses its single valence electron easily, producing hydroxide and hydrogen.


  22. Q: Give reason why oxides of metals are basic.
     A: Metal oxides react with water to form hydroxides which are alkaline.


  23. Q: Give reason why oxides of non-metals are acidic.
     A: Non-metal oxides react with water to form acids.


  24. Q: Give reason why atomic number increases by one across a period.
     A: Each element has one more proton in the nucleus than the previous element.


  25. Q: Give reason why argon is placed before potassium in the modern table.
     A: Argon has atomic number 18 and potassium 19; placement follows atomic number.


  26. Q: Give reason why reactivity of alkaline earth metals is lower than alkali metals.
     A: They have two valence electrons which are held more tightly than one electron in alkali metals.


  27. Q: Give reason why group 1 oxides are more basic than group 2 oxides.
     A: Group 1 metals are more reactive, forming stronger hydroxides.


  28. Q: Give reason why fluorine is the most reactive halogen.
     A: Small size and high electronegativity enable it to gain an electron easily.


  29. Q: Give reason why neon is used in advertising signs.
     A: It is inert, and its glow produces visible light when electrified.


  30. Q: Give reason why helium is used in balloons.
     A: It is lighter than air and non-flammable.


  31. Q: Give reason why elements in the same period have varying chemical properties.
     A: They have different numbers of valence electrons.


  32. Q: Give reason why atomic size decreases across a period but increases down a group.
     A: Across a period, nuclear charge pulls electrons closer; down a group, new shells increase size.


  33. Q: Give reason why metallic character decreases across a period.
     A: Elements on the right tend to gain electrons rather than lose them.


  34. Q: Give reason why non-metallic character increases across a period.
     A: Electrons are more strongly attracted to nucleus on the right side of period.


  35. Q: Give reason why non-metallic character decreases down a group.
     A: Outer electrons are farther from the nucleus, reducing tendency to gain electrons.


  36. Q: Give reason why alkali metals are soft.
     A: Weak metallic bonds due to single valence electron.


  37. Q: Give reason why calcium oxide is basic.
     A: It reacts with water to form calcium hydroxide, a strong base.


  38. Q: Give reason why group 2 metals are harder than group 1 metals.
     A: Stronger metallic bonding due to two valence electrons.


  39. Q: Give reason why Mendeleev predicted properties of undiscovered elements.
     A: Because he observed periodicity and left gaps in his table.


  40. Q: Give reason why hydrogen resembles both alkali metals and halogens.
     A: It has one electron like alkali metals and needs one electron like halogens.


  41. Q: Give reason why lanthanides and actinides are called inner transition elements.
     A: Their f-orbitals are being filled internally while outer s-orbital remains.


  42. Q: Give reason why transition metals are good catalysts.
     A: They can change oxidation states and adsorb reactant molecules.


  43. Q: Give reason why atomic size is smaller in non-metals than metals in the same period.
     A: Higher nuclear charge pulls electrons closer in non-metals.


  44. Q: Give reason why chlorine is more reactive than bromine.
     A: Smaller size and higher electronegativity allow it to gain electrons more easily.


  45. Q: Give reason why elements of group 17 form salts with metals.
     A: Halogens have one valence electron short of octet, reacting with metals to form salts.


  46. Q: Give reason why Mendeleev arranged elements by atomic mass.
     A: Atomic number was not known then, and mass showed periodicity of properties.


  47. Q: Give reason why modern periodic table corrects Mendeleev’s anomalies.
     A: Arranging by atomic number resolves inconsistencies in chemical properties.


  48. Q: Give reason why atomic number is more fundamental than atomic mass.
     A: Chemical properties depend on number of protons, not mass.


  49. Q: Give reason why period 2 elements are smaller in size than period 3 elements.
     A: They have fewer electron shells.


  50. Q: Give reason why alkali metals react with acids.
     A: They easily lose their valence electron to form salts and hydrogen.

Arrange the Words 

Case Studies

  1. Case: A student notices that lithium, sodium, and potassium all react vigorously with water to form hydroxides and hydrogen gas.
     Q1: Identify the group to which these elements belong.
     A1: Group 1 (Alkali metals)

Q2: Explain why they react vigorously with water.
 A2: They have one valence electron, which is easily lost to form hydroxide and hydrogen.



  1. Case: A chemist observes that calcium reacts slowly with water, forming calcium hydroxide and hydrogen.
    Q1: Identify the group of calcium.
     A1: Group 2 (Alkaline earth metals)

Q2: Why is the reaction slower than alkali metals?
A2: Calcium has two valence electrons held more tightly, making the reaction slower.



  1. Case: A school lab has a sample of chlorine gas used for disinfecting water.
    Q1: Which group does chlorine belong to?
     A1: Group 17 (Halogens)

Q2: Why is chlorine highly reactive?
A2: It has seven valence electrons and gains one electron easily to complete its octet.



  1. Case: A gas is collected from a balloon; it is lighter than air and chemically inert.
    Q1: Identify the gas.
     A1: Helium

Q2: Why is helium chemically inert?
A2: It has a complete outer electron shell.



  1. Case: A chemist predicts the existence of an undiscovered element, eka-silicon, based on gaps in Mendeleev’s periodic table.
    Q1: Name the element eventually discovered.
     A1: Germanium

Q2: How was Mendeleev able to predict its properties?
A2: By observing periodic trends in properties of surrounding elements.



  1. Case: Two elements, argon (Z=18) and potassium (Z=19), seem out of order in Mendeleev’s table based on atomic mass.
    Q1: How is this anomaly resolved in the modern periodic table?
     A1: By arranging elements according to atomic number.

Q2: Why is atomic number more reliable than atomic mass?
 A2: Chemical properties depend on the number of protons, not mass.



  1. Case: Copper forms blue solutions in water during lab experiments.
    Q1: Which type of element is copper?
     A1: Transition element

Q2: Why does copper form coloured compounds?
 A2: It has partially filled d-orbitals that absorb visible light.



  1. Case: A student notices helium in balloons and neon in neon lamps.
    Q1: What are these elements collectively called?
     A1: Noble gases

Q2: Why do they rarely form compounds?
A2: They have complete outer electron shells and are chemically stable.



  1. Case: Strontium salts are used to produce red colours in fireworks.
    Q1: To which group does strontium belong?
     A1: Group 2 (Alkaline earth metals)

Q2: Why does it show similar properties to calcium and barium?
 A2: They have the same number of valence electrons (ns²).



  1. Case: Fluorine reacts vigorously with most metals and non-metals.
    Q1: Identify the group of fluorine.
     A1: Group 17 (Halogens)

Q2: Why is fluorine the most reactive halogen?
A2: It has small size and high electronegativity.



  1. Case: Neon, argon, and krypton are used in different types of lighting.
    Q1: What common property do these elements share?
     A1: They are noble gases.

Q2: Why are they suitable for lighting applications?
 A2: They are inert and emit light when electrified.



  1. Case: Sodium and potassium float on water and react violently.
    Q1: Why do these metals float?
     A1: They have low density.

Q2: Why do they react violently with water?
A2: They lose their single valence electron easily, forming hydroxide and hydrogen.



  1. Case: A sample of bromine is stored in a dark bottle.
    Q1: Why is bromine kept in dark bottles?
     A1: To prevent its reaction with light and slow evaporation.

Q2: What is the physical state of bromine at room temperature?
 A2: Liquid



  1. Case: The periodic table shows periodic trends in atomic size.
    Q1: How does atomic size vary across a period?
     A1: It decreases due to increasing nuclear charge.

Q2: How does atomic size vary down a group?
A2: It increases as new electron shells are added.



  1. Case: Calcium reacts with oxygen to form an oxide.
    Q1: What type of oxide is formed?
     A1: Basic oxide

Q2: Why is it basic?
 A2: It reacts with water to form calcium hydroxide.



  1. Case: Halogens react with metals to form salts.
    Q1: Give an example.
     A1: Sodium + Chlorine → Sodium chloride

Q2: Why do halogens form salts with metals?
A2: Halogens gain one electron to complete their octet.



  1. Case: Elements are arranged in periods in the periodic table.
    Q1: What does a period indicate?
     A1: Elements have the same number of electron shells.

Q2: Why do properties change across a period?
 A2: Number of valence electrons increases, altering chemical behaviour.



  1. Case: Lithium, sodium, and potassium form hydroxides with water.
    Q1: Write the general formula of hydroxides formed.
     A1: MOH (M = alkali metal)

Q2: Why are these hydroxides strongly basic?
 A2: They fully dissociate in water to release OH⁻ ions.



  1. Case: Copper and iron act as catalysts in some reactions.
    Q1: Why are transition metals good catalysts?
     A1: They can change oxidation states and adsorb reactant molecules.

Q2: Give an example of a reaction catalyzed by iron.
A2: Haber process for ammonia synthesis.



  1. Case: Modern periodic table resolves issues in Mendeleev’s table.
    Q1: Name one anomaly corrected.
     A1: Placement of argon before potassium.

Q2: Why was Mendeleev’s arrangement by atomic mass insufficient?

A2: It caused chemically dissimilar elements to be placed together.

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