ICSE – Grade 9 – Chemistry – Ch 01 – QA

Questions & Answers

ICSE - Grade - 9

Subject: Chemistry

Chapter - 01 - The Language of Chemistry

Types of Questions

MCQ

  1. What is the chemical symbol of Sodium?
     a) S
     b) So
     c) Na
     d) Sn
     Answer: c) Na



  2. The valency of Oxygen is:
     a) 1
     b) 2
     c) 3
     d) 4
     Answer: b) 2



  3. Which of the following is a polyatomic ion?
     a) Cl⁻
     b) Na⁺
     c) SO₄²⁻
     d) K⁺
     Answer: c) SO₄²⁻



  4. What is the correct formula of Calcium Chloride?
     a) CaCl
     b) CaCl₂
     c) Ca₂Cl
     d) Ca₂Cl₂
     Answer: b) CaCl₂



  5. The Law of Conservation of Mass states that:
     a) Mass is always destroyed in a reaction
     b) Mass is created in chemical reactions
     c) Mass remains constant before and after a reaction
     d) Mass depends on temperature
     Answer: c) Mass remains constant before and after a reaction



  6. What is the charge on the sulphate (SO₄) radical?
     a) -1
     b) -2
     c) +2
     d) 0
     Answer: b) -2



  7.  Which of the following is a balanced equation?
     a) H₂ + O₂ → H₂O
     b) 2H₂ + O₂ → 2H₂O
     c) H₂ + 2O₂ → H₂O₂
     d) H₂O → H₂ + O₂
     Answer: b) 2H₂ + O₂ → 2H₂O



  8. The formula of Ammonium Nitrate is:
     a) NH₃NO₃
     b) NH₄NO₃
     c) NH₂NO₄
     d) NH₃NO₂
     Answer: b) NH₄NO₃



  9. What type of reaction is: Zn + CuSO₄ → ZnSO₄ + Cu?
     a) Combination
     b) Decomposition
     c) Displacement
     d) Double Displacement
     Answer: c) Displacement



  10. What is the valency of Aluminium?
     a) 1
     b) 2
     c) 3
     d) 4
     Answer: c) 3



  11. Which compound contains a covalent bond?
     a) NaCl
     b) H₂O
     c) KBr
     d) MgCl₂
     Answer: b) H₂O



  12. The correct formula for Magnesium Oxide is:
     a) MgO₂
     b) Mg₂O
     c) MgO
     d) Mg₂O₃
     Answer: c) MgO



  13. The radical NO₃⁻ is called:
     a) Nitrite
     b) Nitrate
     c) Hydroxide
     d) Sulphate
     Answer: b) Nitrate



  14. In a balanced equation, the total number of atoms on reactant and product sides should be:
     a) Equal
     b) More on reactant side
     c) More on product side
     d) Cannot be determined
     Answer: a) Equal



  15. The type of reaction where two or more substances combine to form a single product is:
     a) Decomposition
     b) Combination
     c) Displacement
     d) Neutralization
     Answer: b) Combination



  16. Which of the following represents a decomposition reaction?
     a) 2H₂ + O₂ → 2H₂O
     b) 2HgO → 2Hg + O₂
     c) Fe + CuSO₄ → FeSO₄ + Cu
     d) NaCl + AgNO₃ → AgCl + NaNO₃
     Answer: b) 2HgO → 2Hg + O₂



  17. The formula of Ferrous Sulphate is:
     a) FeSO₄
     b) Fe₂SO₄
     c) Fe₂(SO₄)₃
     d) FeS
     Answer: a) FeSO₄



  18. Which element is diatomic in nature?
     a) Neon
     b) Helium
     c) Oxygen
     d) Sodium
     Answer: c) Oxygen



  19. Which of the following is NOT a radical?
     a) SO₄²⁻
     b) OH⁻
     c) Na⁺
     d) H₂
     Answer: d) H₂



  20. What is the charge on the Chloride ion?
     a) +1
     b) -1
     c) -2
     d) +2
     Answer: b) -1



  21. What is the valency of Carbon?  
    a) 2  
    b) 3  
    c) 4  
    d) 5  

                Answer: c) 4



  1. Which of the following is a metal?  
    a) Oxygen  
    b) Nitrogen  
    c) Iron  
    d) Neon  

                Answer: c) Iron


  1. What is the chemical formula of Nitric Acid?  
    a) HNO₂  
    b) HNO₃  
    c) H₂NO₃  
    d) H₂NO₂  

                Answer: b) HNO₃


  1. Which gas is produced in the reaction: Zn + H₂SO₄ → ZnSO₄ + ?  
    a) Oxygen  
    b) Nitrogen  
    c) Hydrogen  
    d) Carbon Dioxide  

                Answer: c) Hydrogen


  1. The formula of Copper(II) Sulphate is:  
    a) CuSO₄  
    b) Cu₂SO₄  
    c) CuS  
    d) Cu₂S  

            Answer: a) CuSO₄  

Fill in the Blanks

  1. The symbol of Potassium is _______.  

   Answer: K  

 

  1. The valency of Carbon in Methane (CH₄) is _______.  

   Answer: 4  

 

  1. The chemical formula of Sulphuric Acid is _______.  

   Answer: H₂SO₄  

 

  1. The radical NO₃⁻ is known as _______.  

   Answer: Nitrate  

 

  1. In a balanced chemical equation, the total number of atoms on both sides must be _______.  

   Answer: Equal  

 

  1. The charge on the Sulphate (SO₄) ion is _______.  

   Answer: -2  

 

  1. The molecular formula of Water is _______.  

   Answer: H₂O  

 

  1. The law that states mass is neither created nor destroyed in a chemical reaction is called _______.  

   Answer: Law of Conservation of Mass  

 

  1. A chemical equation must be _______ to satisfy the law of conservation of mass.  

   Answer: Balanced  

 

  1. The chemical name of NaCl is _______.  

    Answer: Sodium Chloride  

 

  1. The valency of Aluminium is _______.  

    Answer: 3  

 

  1. The formula of Calcium Carbonate is _______.  

    Answer: CaCO₃  

 

  1. The type of reaction where two elements combine to form a compound is called _______.  

    Answer: Combination Reaction  

 

  1. The symbol of Lead is _______.  

    Answer: Pb  

 

  1. The formula for Ammonium Hydroxide is _______.  

    Answer: NH₄OH  

 

  1. The number of Hydrogen atoms in one molecule of Ammonia is _______.  

    Answer: 3  

 

  1. The decomposition of water by electricity is called _______.  

    Answer: Electrolysis  

 

  1. The formula of Ferrous Sulphate is _______.  

    Answer: FeSO₄  

 

  1. The reaction Zn + CuSO₄ → ZnSO₄ + Cu is an example of a _______ reaction.  

    Answer: Displacement  

 

  1. A reaction in which heat is released is called an _______ reaction.  

    Answer: Exothermic  

 

  1. The symbol of Gold is _______.  

    Answer: Au  

 

  1. The valency of Oxygen is _______.  

    Answer: 2  

 

  1. The product formed when Hydrogen burns in Oxygen is _______.  

    Answer: Water (H₂O)  

 

  1. The molecular formula of Oxygen gas is _______.  

    Answer: O₂  

 

  1. The positively charged ion is called a _______.  

    Answer: Cation  

 

  1. The negatively charged ion is called an _______.  

    Answer: Anion  

 

  1. The symbol of Iron is _______.  

    Answer: Fe  

 

  1. The charge on the Chloride ion (Cl⁻) is _______.  

    Answer: -1  

 

  1. A reaction in which a compound breaks down into simpler substances is called a _______ reaction.  

    Answer: Decomposition  

 

  1. The formula of Hydrochloric Acid is _______.  

    Answer: HCl  

 

  1. The gas released when Zinc reacts with Hydrochloric Acid is _______.  

    Answer: Hydrogen  

 

  1. The formula of Sodium Carbonate is _______.  

    Answer: Na₂CO₃  

 

  1. A reaction where two compounds exchange their ions is called a _______ reaction.  

    Answer: Double Displacement  

 

  1. The number of Oxygen atoms in Sulphuric Acid (H₂SO₄) is _______.  

    Answer: 4  

 

  1. The charge on the Nitrate ion (NO₃⁻) is _______.  

    Answer: -1  

 

  1. The element with atomic number 1 is _______.  

    Answer: Hydrogen  

 

  1. The reaction 2H₂ + O₂ → 2H₂O is an example of a _______ reaction.  

    Answer: Combination  

 

  1. The molecular formula of Carbon Dioxide is _______.  

    Answer: CO₂  

 

  1. The symbol of Mercury is _______.  

    Answer: Hg  

 

  1. The process of balancing a chemical equation ensures the _______ of mass.  

    Answer: Conservation  

 

  1. The formula for Sodium Hydroxide is _______.  

    Answer: NaOH  

 

  1. A reaction that absorbs heat is called an _______ reaction.  

    Answer: Endothermic  

 

  1. The formula for Magnesium Chloride is _______.  

    Answer: MgCl₂  

 

  1. A compound containing only two elements is called a _______ compound.  

    Answer: Binary  

 

  1. The radical OH⁻ is known as _______.  

    Answer: Hydroxide  

 

  1. The number of Hydrogen atoms in one molecule of Sulphuric Acid (H₂SO₄) is _______.  

    Answer: 2  

 

  1. The formula for Calcium Hydroxide is _______.  

    Answer: Ca(OH)₂  

 

  1. The process of gaining oxygen in a reaction is called _______.  

    Answer: Oxidation  

 

  1. The process of losing oxygen in a reaction is called _______.  

    Answer: Reduction  

 

  1. The reaction Fe + S → FeS is an example of a _______ reaction.  

    Answer: Combination  

Name the Following

  1. The symbol of Sodium.  

   Answer: Na  

 

  1. The valency of Oxygen.  

   Answer: 2  

 

  1. The molecular formula of Water.  

   Answer: H₂O  

 

  1. The scientist who proposed the Law of Conservation of Mass.  

   Answer: Antoine Lavoisier  

 

  1. The type of reaction where heat is released.  

   Answer: Exothermic Reaction  

 

  1. The charge on a Sulphate ion (SO₄²⁻).  

   Answer: -2  

 

  1. The positively charged ion.  

   Answer: Cation  

 

  1. The negatively charged ion.  

   Answer: Anion  

 

  1. The formula of Ammonium Hydroxide.  

   Answer: NH₄OH  

 

  1. The process in which water is decomposed into Hydrogen and Oxygen by electricity.  

    Answer: Electrolysis  

 

  1. The molecular formula of Carbon Dioxide.  

    Answer: CO₂  

 

  1. The formula of Hydrochloric Acid.  

    Answer: HCl  

 

  1. The charge on a Nitrate ion (NO₃⁻).  

    Answer: -1  

 

  1. The reaction in which a single substance breaks down into two or more simpler substances.  

    Answer: Decomposition Reaction  

 

  1. The scientist who introduced symbols for elements.  

    Answer: John Dalton  

 

  1. The formula for Sodium Carbonate.  

    Answer: Na₂CO₃  

 

  1. The symbol of Lead.  

    Answer: Pb  

 

  1. The formula of Sulphuric Acid.  

    Answer: H₂SO₄  

 

  1. The reaction where two elements combine to form a compound.  

    Answer: Combination Reaction  

 

  1. The gas released when Zinc reacts with Hydrochloric Acid.  

    Answer: Hydrogen  

 

  1. The molecular formula of Oxygen gas.  

    Answer: O₂  

 

  1. The process of balancing a chemical equation ensures this law.  

    Answer: Law of Conservation of Mass  

 

  1. The formula for Calcium Hydroxide.  

    Answer: Ca(OH)₂  

 

  1. The process of gaining oxygen in a reaction.  

    Answer: Oxidation  

 

  1. The process of losing oxygen in a reaction.  

    Answer: Reduction  

 

  1. The formula of Ferric Chloride.  

    Answer: FeCl₃  

 

  1. The type of reaction where two compounds exchange their ions.  

    Answer: Double Displacement Reaction  

 

  1. The formula of Magnesium Chloride.  

    Answer: MgCl₂  

 

  1. The compound that contains only two elements.  

    Answer: Binary Compound  

 

  1. The radical OH⁻ is called.  

    Answer: Hydroxide  

 

  1. The molecular formula of Ammonia.  

    Answer: NH₃  

 

  1. The metal which reacts with water to form Hydrogen gas.  

    Answer: Sodium  

 

  1. The type of reaction Zn + CuSO₄ → ZnSO₄ + Cu represents.  

    Answer: Displacement Reaction  

 

  1. The gas used in balloons due to its lightness.  

    Answer: Helium  

 

  1. The scientist who proposed atomic theory.  

    Answer: John Dalton  

 

  1. The formula of Calcium Carbonate.  

    Answer: CaCO₃  

 

  1. The process of heat absorption during a reaction.  

    Answer: Endothermic Reaction  

 

  1. The charge on a Chloride ion (Cl⁻).  

    Answer: -1  

 

  1. The metal whose symbol is Fe.  

    Answer: Iron  

 

  1. The gas essential for combustion.  

    Answer: Oxygen  

 

  1. The formula of Sodium Hydroxide.  

    Answer: NaOH  

 

  1. The symbol of Silver.  

    Answer: Ag  

 

  1. The reaction Fe + S → FeS is an example of this type of reaction.  

    Answer: Combination Reaction  

 

  1. The law that states elements combine in fixed ratios by mass.  

    Answer: Law of Constant Proportion  

 

  1. The molecular formula of Methane.  

    Answer: CH₄  

 

  1. The reaction type in which an acid reacts with a base to form salt and water.  

    Answer: Neutralization Reaction  

 

  1. The formula of Nitric Acid.  

    Answer: HNO₃  

 

  1. The metal whose symbol is Hg.  

    Answer: Mercury  

 

  1. The radical CO₃²⁻ is known as.  

    Answer: Carbonate  

 

  1. The simplest form of matter that cannot be broken down further by chemical means.  

    Answer: Element  

Answer in One Word

  1. The symbol of Potassium.  

   Answer: K  

 

  1. The molecular formula of Oxygen gas.  

   Answer: O₂  

 

  1. The scientist who proposed the atomic theory.  

   Answer: Dalton  

 

  1. The charge on a Sulphate ion (SO₄²⁻).  

   Answer: -2  

 

  1. The formula of Hydrochloric Acid.  

   Answer: HCl  

 

  1. The metal whose symbol is Fe.  

   Answer: Iron  

 

  1. The reaction in which heat is released.  

   Answer: Exothermic  

 

  1. The process of decomposition of water by electricity.  

   Answer: Electrolysis  

 

  1. The positively charged ion.  

   Answer: Cation  

 

  1. The formula of Sodium Carbonate.  

    Answer: Na₂CO₃  

 

  1. The law that states mass is conserved in a chemical reaction.  

    Answer: Conservation  

 

  1. The radical OH⁻ is known as.  

    Answer: Hydroxide  

 

  1. The reaction where two elements combine to form a compound.  

    Answer: Combination  

 

  1. The gas released when Zinc reacts with Hydrochloric Acid.  

    Answer: Hydrogen  

 

  1. The formula of Ammonium Hydroxide.  

    Answer: NH₄OH  

 

  1. The charge on a Nitrate ion (NO₃⁻).  

    Answer: -1  

 

  1. The reaction where a compound breaks into simpler substances.  

    Answer: Decomposition  

 

  1. The symbol of Gold.  

    Answer: Au  

 

  1. The valency of Aluminium.  

    Answer: 3  

 

  1. The type of ion formed by non-metals.  

    Answer: Anion  

 

  1. The scientist who introduced element symbols.  

    Answer: Dalton  

 

  1. The gas essential for combustion.  

    Answer: Oxygen  

 

  1. The process of balancing a chemical equation ensures this law.  

    Answer: Conservation  

 

  1. The metal with symbol Pb.  

    Answer: Lead  

 

  1. The type of reaction Zn + CuSO₄ → ZnSO₄ + Cu represents.  

    Answer: Displacement  

 

  1. The formula of Magnesium Chloride.  

    Answer: MgCl₂  

 

  1. The charge on a Chloride ion (Cl⁻).  

    Answer: -1  

 

  1. The process of gaining oxygen in a reaction.  

    Answer: Oxidation  

 

  1. The formula of Sodium Hydroxide.  

    Answer: NaOH  

 

  1. The reaction Fe + S → FeS is an example of this type of reaction.  

    Answer: Combination  

 

  1. The scientist who introduced the Law of Conservation of Mass.  

    Answer: Lavoisier  

 

  1. The symbol of Silver.  

    Answer: Ag  

 

  1. The molecular formula of Water.  

    Answer: H₂O  

 

  1. The metal with atomic number 1.  

    Answer: Hydrogen  

 

  1. The formula of Nitric Acid.  

    Answer: HNO₃  

 

  1. The process of losing oxygen in a reaction.  

    Answer: Reduction  

 

  1. The simplest form of matter.  

    Answer: Element  

 

  1. The formula of Ferric Chloride.  

    Answer: FeCl₃  

 

  1. The reaction in which two compounds exchange their ions.  

    Answer: Double-displacement  

 

  1. The formula of Sulphuric Acid.  

    Answer: H₂SO₄  

 

  1. The gas used in balloons due to its lightness.  

    Answer: Helium  

 

  1. The valency of Oxygen.  

    Answer: 2  

 

  1. The formula of Calcium Hydroxide.  

    Answer: Ca(OH)₂  

 

  1. The process of heat absorption during a reaction.  

    Answer: Endothermic  

 

  1. The law that states elements combine in fixed ratios by mass.  

    Answer: Proportion  

 

  1. The radical CO₃²⁻ is known as.  

    Answer: Carbonate  

 

  1. The formula of Calcium Carbonate.  

    Answer: CaCO₃  

 

  1. The molecular formula of Carbon Dioxide.  

    Answer: CO₂  

 

  1. The charge on an Aluminium ion.  

    Answer: +3  

 

  1. The simplest type of chemical reaction.  

    Answer: Combination  

ICSE - Grade 9 - Physics

All Chapters

  • Chapter 1 Measurement and Experimentation
  • Chapter 2 Motion in one dimension
  • Chapter 3 Laws of Motion
  • Chapter 4 Pressure in fluids and Atmospheric pressure
  • Chapter 5 Upthrust in Fluids, Archimedes’ Principle and Floatation
  • Chapter 6 Heat and energy
  • Chapter 7 Reflection of light
  • Chapter 8 Propagation of Sound waves
  • Chapter 9 Current Electricity
  • Chapter 10 Magnetism

ICSE - Grade 9 - Chemistry

All Chapters

  • Chapter 1 The Language of Chemistry
  • Chapter 2 Chemical Changes and Reactions
  • Chapter 3 Water
  • Chapter 4 Atomic Structure and Chemical Bonding
  • Chapter 5 The periodic table
  • Chapter 6 Study of the first Element Hydrogen
  • Chapter 7 Study of Gas laws
  • Chapter 8 Atmospheric Pollution

ICSE - Grade 9 - Mathematics

All Chapters

  • Chapter 1 Rational and Irrational Numbers
  • Chapter 2 Compound Interest [Without Using Formula]
  • Chapter 3 Compound Interest [Using Formula]
  • Chapter 4 Expansions
  • Chapter 5 Factorisation
  • Chapter 6 Simultaneous Equations
  • Chapter 7 Indices
  • Chapter 8 Logarithms
  • Chapter 9 Triangles
  • Chapter 10 Isosceles Triangles
  • Chapter 11 Inequalities
  • Chapter 12 Midpoint and Its Converse
  • Chapter 13 Pythagoras Theorem
  • Chapter 14 Rectilinear Figures
  • Chapter 15 Construction of Polygons
  • Chapter 16 Area Theorems
  • Chapter 17 Circle
  • Chapter 18 Statistics
  • Chapter 19 Mean and Median
  • Chapter 20 Area and Perimeter of Plane Figures
  • Chapter 21 Solids
  • Chapter 22 Trigonometrical Ratios
  • Chapter 23 Trigonometrical Ratios of Standard Angles
  • Chapter 24 Solutions of Right Triangles
  • Chapter 25 Complementary Angles
  • Chapter 26 Coordinate Geometry
  • Chapter 27 Graphical Solution
  • Chapter 28 Distance Formula

ICSE - Grade 9 - Biology

All Chapters

  • Chapter 1 Introducing Biology
  • Chapter 2 Cell: The Unit Of Life
  • Chapter 3 Tissues: Plant And Animal Tissue
  • Chapter 4 The Flower
  • Chapter 5 Pollination and Fertilization
  • Chapter 6 Seeds: Structure and Germination
  • Chapter 7 Respiration in Plants
  • Chapter 8 Five Kingdom Classification
  • Chapter 9 Economic Importance of Bacteria and Fungi
  • Chapter 10 Nutrition
  • Chapter 11 Digestive system
  • Chapter 12 Skeleton: Movement and Locomotion
  • Chapter 13 Skin: The Jack of all trades
  • Chapter 14 The Respiratory System
  • Chapter 15 Hygiene: [A key to Healthy Life]
  • Chapter 16 Diseases: Cause and Control
  • Chapter 17 Aids to Health
  • Chapter 18 Health Organizations
  • Chapter 19 Waste Generation and Management

ICSE - Grade 9 - History

All Chapters

  • Chapter 1 – The Harappan Civilisation
  • Chapter 2 – The Vedic Period
  • Chapter 3 – Jainism and Buddhism
  • Chapter 4 – The Mauryan Empire
  • History — Chapter 5
    The Sangam Age
  • Chapter 6 – The Age of the Guptas
  • Chapter 7 – Medieval India — (A) The Cholas
  • Chapter 8 – Medieval India — (B) The Delhi Sultanate
  • Chapter 9 – Medieval India — (C) The Mughal Empire
  • Chapter 10 – Medieval India — (D) Composite Culture
  • Chapter 11 – The Modern Age in Europe — (A) Renaissance
  • Chapter 12 – The Modern Age in Europe — (B) Reformation
  • Chapter 13 – The Modern Age in Europe — (C) Industrial Revolution
  •  

ICSE - Grade 9 - Civics

All Chapters

  • Chapter 1: Our Constitution
  • Chapter 2: Salient Features of the Constitution — I
  • Chapter 3: Salient Features of the
  • Constitution — II
  • Chapter 4: Elections
  • Chapter 5: Local Self-Government — Rural
  • Chapter 6: Local Self-Government — Urban
  •  

ICSE - Grade 9 - Geography

All Chapters

  • Ch 1 – Earth as a Planet
    Ch 2 – Geographic Grid: Latitudes and Longitudes
    Ch 3 – Rotation and Revolution
    Ch 4 – Earth’s Structure
    Ch 5 – Landforms of the Earth
    Ch 6 – Rocks
    Ch 7 – Volcanoes
    Ch 8 – Earthquakes
    Ch 9 – Weathering
    Ch 10 – Denudation
    Ch 11 – Hydrosphere
    Ch 12 – Composition and Structure of the Atmosphere
    Ch 13 – Insolation
    Ch 14 – Atmospheric Pressure and Winds
    Ch 15 – Humidity
    Ch 16 – Pollution
    Ch 17 – Sources of Pollution
    Ch 18 – Effects of Pollution
    Ch 19 – Preventive Measures
    Ch 20 – Natural Regions of the World

ICSE Grade 9

3500/-
  • All Subjects
  • Free Study Material
  • MCQ Tests
  • Theory Tests
  • Assignments
Register

Find the Odd Man Out

  1. Na, K, Ca, Cl  

   Answer: Cl (Others are metals)  

 

  1. H₂O, CO₂, O₂, CH₄  

   Answer: O₂ (Others are compounds, O₂ is an element)  

 

  1. Fe, Cu, Ag, He  

   Answer: He (Others are metals, He is a noble gas)  

 

  1. NO₃⁻, SO₄²⁻, Cl⁻, Na⁺  

   Answer: Na⁺ (Others are negatively charged ions)  

 

  1. H₂SO₄, HCl, NaOH, HNO₃  

   Answer: NaOH (Others are acids, NaOH is a base)  

 

  1. Zn, Al, Pb, Br  

   Answer: Br (Others are metals, Br is a non-metal)  

 

  1. Oxygen, Hydrogen, Carbon, Sodium  

   Answer: Sodium (Others are non-metals)  

 

  1. Oxidation, Reduction, Electrolysis, Endothermic  

   Answer: Electrolysis (Others describe chemical reactions, Electrolysis is a process)  

 

  1. Ca(OH)₂, NaOH, KOH, H₂SO₄  

   Answer: H₂SO₄ (Others are bases, H₂SO₄ is an acid)  

 

  1. C, N, O, Fe  

    Answer: Fe (Others are non-metals)  

 

  1. CO₂, NH₃, CH₄, FeO  

    Answer: FeO (Others are gaseous molecules, FeO is a solid compound)  

 

  1. Zn, Cu, Fe, O₂  

    Answer: O₂ (Others are metals, O₂ is a gas)  

 

  1. Cl₂, O₂, N₂, H₂O  

    Answer: H₂O (Others are diatomic elements, H₂O is a compound)  

 

  1. NaCl, H₂O, CO₂, He  

    Answer: He (Others are compounds, He is an element)  

 

  1. H₂, N₂, Na, Cl₂  

    Answer: Na (Others are diatomic molecules, Na is a metal)  

 

  1. H₂O, NaCl, HCl, O₂  

    Answer: O₂ (Others are compounds, O₂ is an element)  

 

  1. CaCO₃, NaHCO₃, CO₂, H₂O  

    Answer: CO₂ (Others are solid compounds, CO₂ is a gas)  

 

  1. Na, K, Fe, Cl  

    Answer: Cl (Others are metals, Cl is a non-metal)  

 

  1. NH₄⁺, SO₄²⁻, NO₃⁻, Cl⁻  

    Answer: NH₄⁺ (Others are anions, NH₄⁺ is a cation)  

 

  1. CuSO₄, FeCl₃, NaOH, AgNO₃  

    Answer: NaOH (Others are salts, NaOH is a base)  

 

  1. Exothermic, Endothermic, Reduction, Oxidation  

    Answer: Endothermic (Others involve electron transfer, Endothermic relates to heat absorption)  

 

  1. ZnCl₂, MgO, Al₂O₃, CO₂  

    Answer: CO₂ (Others are metal oxides, CO₂ is a non-metal oxide)  

 

  1. NaCl, KCl, NH₄OH, CaCl₂  

    Answer: NH₄OH (Others are salts, NH₄OH is a base)  

 

  1. CuSO₄, NaOH, MgCl₂, KNO₃  

    Answer: NaOH (Others are salts, NaOH is a base)  

 

  1. Acid, Base, Salt, Alloy  

    Answer: Alloy (Others are chemical compounds, Alloy is a mixture)  

 

  1. O₂, H₂, Cl₂, HCl  

    Answer: HCl (Others are diatomic molecules, HCl is a compound)  

 

  1. Rusting, Electrolysis, Combustion, Corrosion  

    Answer: Electrolysis (Others are natural processes, Electrolysis is a controlled process)  

 

  1. H₂O, CO₂, HCl, NaOH  

    Answer: NaOH (Others are acids or neutral compounds, NaOH is a base)  

 

  1. Zn, Fe, Al, CO₂  

    Answer: CO₂ (Others are metals, CO₂ is a gas)  

 

  1. Cation, Anion, Molecule, Radical  

    Answer: Molecule (Others are charged species, Molecule is neutral)  

 

  1. Water, Alcohol, Hydrochloric Acid, Sodium  

    Answer: Sodium (Others are liquids, Sodium is a metal)  

 

  1. ZnO, Fe₂O₃, CuO, H₂SO₄  

    Answer: H₂SO₄ (Others are metal oxides, H₂SO₄ is an acid)  

 

  1. CH₄, NH₃, CO₂, FeO  

    Answer: FeO (Others are gaseous compounds, FeO is a solid)  

 

  1. Na⁺, K⁺, Mg²⁺, Cl⁻  

    Answer: Cl⁻ (Others are positively charged ions)  

 

  1. Hydrogen, Oxygen, Carbon, Sodium  

    Answer: Sodium (Others are non-metals, Sodium is a metal)  

 

  1. Cu, Fe, Al, NaCl  

    Answer: NaCl (Others are metals, NaCl is a compound)  

 

  1. Mg, Al, Fe, O₂  

    Answer: O₂ (Others are metals, O₂ is a gas)  

 

  1. Ca(OH)₂, NaOH, KOH, HNO₃  

    Answer: HNO₃ (Others are bases, HNO₃ is an acid)  

 

  1. H₂, O₂, N₂, Na  

    Answer: Na (Others are gases, Na is a metal)  

 

  1. FeS, NaCl, H₂O, Cl₂  

    Answer: Cl₂ (Others are compounds, Cl₂ is an element)  

 

  1. Electrolysis, Reduction, Oxidation, Corrosion  

    Answer: Electrolysis (Others are spontaneous reactions, Electrolysis is non-spontaneous)  

 

  1. K, Na, Li, Cl₂  

    Answer: Cl₂ (Others are alkali metals, Cl₂ is a non-metal)  

 

  1. Neutralization, Double displacement, Decomposition, Oxidation  

    Answer: Decomposition (Others involve chemical exchange, Decomposition involves breakdown)  

 

  1. NH₃, H₂S, HCl, NaOH  

    Answer: NaOH (Others are acids, NaOH is a base)  

 

  1. Zn, Cu, Fe, H₂  

    Answer: H₂ (Others are metals, H₂ is a gas)  

 

  1. H₂O, CO₂, SO₂, NaOH  

    Answer: NaOH (Others are oxides, NaOH is a base)  

 

  1. NaCl, KCl, NH₄Cl, HCl  

    Answer: HCl (Others are salts, HCl is an acid)  

 

  1. Rusting, Photosynthesis, Electrolysis, Combustion  

    Answer: Photosynthesis (Others involve oxidation, Photosynthesis is a biological process)  

 

  1. NH₄⁺, SO₄²⁻, NO₃⁻, Cl⁻  

    Answer: NH₄⁺ (Others are anions, NH₄⁺ is a cation)  

 

  1. O₂, N₂, CO₂, H₂  

    Answer: CO₂ (Others are elemental gases, CO₂ is a compound)  

Match the Pair

Set 1: Match the Pair

  1. H₂O                         – (a) Sodium chloride  
  2. CO₂                         – (b) Hydrochloric acid  
  3. NaCl                        – (c) Carbon dioxide  
  4. HCl                         – (d) Water  
  5. O₂                          – (e) Oxygen  

 

Correct Answers:

1 – d  

2 – c  

3 – a  

4 – b  

5 – e  

 

Set 2: Match the Pair

  1. Law of Conservation of Mass  – (a) Antoine Lavoisier  
  2. Chemical formula             – (b) Symbolic representation of a compound  
  3. Balanced equation            – (c) Follows the Law of Conservation of Mass  
  4. Atomic mass unit (amu)       – (d) Unit to express atomic mass  
  5. Valency                      – (e) Combining capacity of an element  

 

Correct Answers:

1 – a  

2 – b  

3 – c  

4 – d  

5 – e  

 

Set 3: Match the Pair

  1. Decomposition reaction       – (a) Combination reaction  
  2. 2H₂ + O₂ → 2H₂O              – (b) Decomposition reaction  
  3. CaCO₃ → CaO + CO₂            – (c) Redox reaction  
  4. Fe + CuSO₄ → FeSO₄ + Cu      – (d) Displacement reaction  
  5. Mg + O₂ → MgO                – (e) Combination reaction  

 

Correct Answers:

1 – b  

2 – e  

3 – a  

4 – d  

5 – c  

 

Set 4: Match the Pair

  1. Acid                         – (a) pH more than 7  
  2. Base                         – (b) Releases H⁺ ions  
  3. Neutralization               – (c) Salt and water formation  
  4. H₂SO₄                        – (d) Sulfuric acid  
  5. NaOH                         – (e) Sodium hydroxide  

 

Correct Answers:

1 – b  

2 – a  

3 – c  

4 – d  

5 – e  

 

Set 5: Match the Pair

  1. Catalyst                     – (a) Energy required to start a reaction  
  2. Exothermic reaction           – (b) Releases heat  
  3. Activation energy             – (c) Alters reaction rate without getting consumed  
  4. Endothermic reaction          – (d) Absorbs heat  
  5. Zn + HCl → ZnCl₂ + H₂         – (e) Single displacement reaction  

 

Correct Answers:

1 – c  

2 – b  

3 – a  

4 – d  

5 – e  

 

Set 6: Match the Pair

  1. Symbol of iron               – (a) N  
  2. Symbol of nitrogen           – (b) Fe  
  3. Chemical name of baking soda – (c) Sodium bicarbonate  
  4. CuSO₄                        – (d) Copper sulfate  
  5. H₂O₂                         – (e) Hydrogen peroxide  

 

Correct Answers:

1 – b  

2 – a  

3 – c  

4 – d  

5 – e  

 

Set 7: Match the Pair

  1. Avogadro’s number            – (a) 6.022 × 10²³  
  2. Atomic number of oxygen      – (b) 8  
  3. Molar mass of H₂O            – (c) 18 g/mol  
  4. Mole                         – (d) Amount containing Avogadro’s number of particles  
  5. Atomic number of carbon      – (e) 6  

 

Correct Answers:

1 – a  

2 – b  

3 – c  

4 – d  

5 – e  

 

Set 8: Match the Pair

  1. NaOH                         – (a) Hydrochloric acid  
  2. HCl                          – (b) Sodium hydroxide  
  3. Neutral solution             – (c) pH = 7  
  4. Lime water                   – (d) Ca(OH)₂  
  5. HNO₃                         – (e) Nitric acid  

 

Correct Answers:

1 – b  

2 – a  

3 – c  

4 – d  

5 – e  

 

Set 9: Match the Pair

  1. Reactant                     – (a) Substance formed in a reaction  
  2. Product                      – (b) Substance that reacts  
  3. Coefficient                  – (c) Number of molecules in a reaction  
  4. Subscript                    – (d) Number of atoms in a molecule  
  5. Balanced chemical equation   – (e) Follows conservation of mass  

 

Correct Answers:

1 – b  

2 – a  

3 – c  

4 – d  

5 – e  

 

Set 10: Match the Pair

  1. CO                           – (a) Carbon dioxide  
  2. CO₂                          – (b) Carbon monoxide  
  3. NH₃                          – (c) Ammonia  
  4. SO₂                          – (d) Sulfur dioxide  
  5. CH₄                          – (e) Methane  

 

Correct Answers:

1 – b  

2 – a  

3 – c  

4 – d  

5 – e  

Short Answer Questions  

  1. Define a chemical symbol.  

   Answer: A chemical symbol is a one or two-letter representation of an element.  

 

  1. What is the valency of oxygen?  

   Answer: The valency of oxygen is 2.  

 

  1. Write the molecular formula of water.  

Answer: H₂O  

 

  1. State the Law of Conservation of Mass.  

 Answer: Mass can neither be created nor destroyed in a chemical reaction.  

 

  1. What is the atomic number of carbon?  

Answer: 6  

 

  1. Write the formula of sulfuric acid.  

  Answer: H₂SO₄  

 

  1. What is the molar mass of CO₂?  

  Answer: 44 g/mol  

 

  1. Give an example of a diatomic molecule.  

Answer: O₂ or H₂  

 

  1. What is a balanced chemical equation?  

Answer: An equation where the number of atoms of each element is equal on both sides.  

 

  1. Write the formula for ammonium sulfate.  

Answer: (NH₄)₂SO₄  

 

  1. What is the chemical name of quicklime?  

Answer: Calcium oxide (CaO)  

 

  1. Name the scientist who proposed the atomic theory.  

    Answer: John Dalton  

 

  1. What is the formula of common salt?  

   Answer: NaCl  

 

  1. Define a compound.  

   Answer: A compound is a substance formed by the chemical combination of two or more elements in fixed proportions.  

 

  1. What is the valency of sodium?  

 Answer: 1  

 

  1. What is the molecular formula of methane?  

Answer: CH₄  

 

  1. Write the formula for hydrochloric acid.  

   Answer: HCl  

 

  1. What is a reactant?  

Answer: A substance that takes part in a chemical reaction.  

 

  1. What is a product in a chemical reaction?  

    – A substance formed as a result of a chemical reaction.  

 

  1. What is a polyatomic ion?  

 Answer: A charged species composed of two or more atoms.  

 

  1. Give an example of a polyatomic ion.  

 Answer: SO₄²⁻ (Sulfate ion)  

 

  1. Write the chemical formula of lime water.  

   Answer: Ca(OH)₂  

 

  1. What is a molecular formula?  

   Answer: A formula that shows the exact number of atoms of each element in a molecule.  

 

  1. What is an empirical formula?  

Answer: The simplest whole-number ratio of elements in a compound.  

 

  1. Write an example of a decomposition reaction.  

Answer: 2H₂O → 2H₂ + O₂  

 

  1. What is an exothermic reaction?  

    – A reaction that releases heat energy.  

 

  1. What is an endothermic reaction?  

Answer: A reaction that absorbs heat energy.  

 

  1. Write the balanced equation for the reaction of hydrogen and oxygen to form water.  

   Answer: 2H₂ + O₂ → 2H₂O  

 

  1. What is the chemical formula of nitric acid?  

 Answer: HNO₃  

 

  1. What is Avogadro’s number?  

  Answer: 6.022 × 10²³  

 

  1. What is the pH of a neutral solution?  

 Answer: 7  

 

  1. Write the molecular formula of glucose.  

 Answer: C₆H₁₂O₆  

 

  1. What is the charge on a chloride ion?  

Answer: -1  

 

  1. Define atomic mass.  

Answer: The mass of an atom compared to 1/12th of the mass of a carbon-12 atom.  

 

  1. Name a metal that reacts with acid to produce hydrogen gas.  

Answer: Zinc (Zn)  

 

  1. What is a covalent bond?  

 Answer: A bond formed by the sharing of electrons between atoms.  

 

  1. What is an ionic bond?  

Answer: A bond formed due to the transfer of electrons from one atom to another.  

 

  1. What is the formula for calcium chloride?  

   Answer: CaCl₂  

 

  1. Write an example of a combination reaction.  

  Answer: 2Mg + O₂ → 2MgO  

 

  1. What is a mole?  

 Answer: A mole is the amount of a substance containing Avogadro’s number of particles.  

 

  1. What is a catalyst?  

Answer: A substance that increases the rate of a reaction without being consumed.  

 

  1. What is the chemical formula of baking soda?  

Answer: NaHCO₃  

 

  1. What is the valency of aluminum?  

Answer: 3  

 

  1. What is the charge on a sulfate ion (SO₄²⁻)?  

Answer: -2  

 

  1. What is a chemical reaction?  

Answer: A process in which substances change to form new substances.  

 

  1. What is the molecular mass of H₂O?  

Answer: 18 g/mol  

 

  1. Write the balanced equation for the reaction of calcium carbonate decomposition.  

Answer: CaCO₃ → CaO + CO₂  

 

  1. What is the formula for ferrous sulfate?  

Answer: FeSO₄  

 

  1. Name a noble gas.  

Answer: Helium (He)  

 

  1. What is the molecular formula of ethanol?  

Answer: C₂H₅OH  

Puzzles

  1. I am a gas that turns limewater milky. Who am I?  

   Answer: Carbon dioxide (CO₂)  

 

  1. I am a metal that reacts violently with water. Who am I?  

   Answer: Sodium (Na)  

 

  1. My atomic number is 8, and I am essential for life. Who am I?  

   Answer: Oxygen (O)  

 

  1. I am the simplest element with one proton and one electron. Who am I?  

   Answer: Hydrogen (H)  

 

  1. I am the process of losing electrons in a reaction. What am I?  

  Answer: Oxidation  

 

  1. I am the law stating mass is neither created nor destroyed in a chemical reaction. What am I?  

  Answer: Law of Conservation of Mass  

 

  1. I am the scientist who introduced symbols for elements. Who am I?  

   Answer: John Dalton  

 

  1. I am the compound that gives fizz to soft drinks. What am I?  

   Answer: Carbon dioxide (CO₂)  

 

  1. I am the type of bond formed between metals and non-metals. What am I?  

   Answer: Ionic bond  

 

  1. I am the process where solid changes to gas directly. What am I?  

    Answer: Sublimation  

 

  1. I am the atomic number of chlorine. What am I?  

    Answer: 17  

 

  1. I am the chemical name of rust. What am I?  

   Answer: Iron(III) oxide (Fe₂O₃·xH₂O)  

 

  1. I am the gas evolved when magnesium reacts with acid. What am I?  

    Answer: Hydrogen (H₂)  

 

  1. I am the symbol of an element that is a liquid metal. What am I?  

   Answer: Hg (Mercury)  

 

  1. I am the simplest form of a substance that cannot be broken down further. What am I?  

   Answer: Element  

 

  1. I am the process in which two or more substances combine to form a new one. What am I?  

   Answer: Chemical combination  

 

  1. I am the representation of a chemical reaction using symbols and formulae. What am I?  

   Answer: Chemical equation  

 

  1. I am a molecule with the formula H₂O₂. What am I?  

   Answer: Hydrogen peroxide  

 

  1. I am the scientist who developed the Periodic Table. Who am I?  

   Answer: Dmitri Mendeleev  

 

  1. I am a diatomic gas essential for combustion. What am I?  

   Answer: Oxygen (O₂)  

 

  1. I am the smallest particle of an element. What am I?  

   Answer: Atom  

 

  1. I am the pH value of pure water. What am I?  

   Answer: 7  

 

  1. I am the name of the reaction where heat is absorbed. What am I?  

   Answer: Endothermic reaction  

 

  1. I am a non-metal that conducts electricity. What am I?  

   Answer: Graphite  

 

  1. I am the process of balancing a chemical equation. What am I?  

   Answer: Law of Conservation of Mass  

 

  1. I am the scientist who discovered oxygen. Who am I?  

   Answer: Joseph Priestley  

 

  1. I am the metal used in making aircraft due to my lightweight nature. What am I?  

   Answer: Aluminium (Al)  

 

  1. I am a gas that supports combustion but does not burn. What am I?  

   Answer: Oxygen (O₂)  

 

  1. I am the common name for sodium chloride. What am I?  

   Answer: Table salt  

 

  1. I am a liquid that turns red litmus paper blue. What am I?  

   Answer: Base  

 

  1. I am the type of reaction in which a compound breaks into simpler substances. What am I?  

   Answer: Decomposition reaction  

 

  1. I am the force that holds atoms together in a molecule. What am I?  

   Answer: Chemical bond  

 

  1. I am a gas released when an acid reacts with a carbonate. What am I?  

   Answer: Carbon dioxide (CO₂)  

 

  1. I am the symbol for an element used in making electric wires. What am I?  

   Answer: Cu (Copper)  

 

  1. I am the process in which a gas changes into a liquid. What am I?  

   Answer: Condensation  

 

  1. I am the type of bond in water molecules. What am I?  

   Answer: Covalent bond  

 

  1. I am the most abundant gas in Earth’s atmosphere. What am I?  

   Answer: Nitrogen (N₂)  

 

  1. I am the chemical name of quicklime. What am I?  

   Answer: Calcium oxide (CaO)  

 

  1. I am the term used for substances that increase the rate of a chemical reaction. What am I?  

   Answer: Catalyst  

 

  1. I am the scientist who discovered electrons. Who am I?  

   Answer: J.J. Thomson  

 

  1. I am the unit used to measure atomic mass. What am I?  

   – Answer: Atomic mass unit (amu)  

 

  1. I am the gas evolved when dilute sulfuric acid reacts with zinc. What am I?  

   Answer: Hydrogen (H₂)  

 

  1. I am the term for substances that prevent rusting. What am I?  

   Answer: Anti-corrosives  

 

  1. I am the term for elements in Group 18 of the periodic table. What am I?  

   Answer: Noble gases  

 

  1. I am the name of a reaction where energy is released. What am I?  

   Answer: Exothermic reaction  

 

  1. I am the metal that burns with a white dazzling flame. What am I?  

   Answer: Magnesium (Mg)  

 

  1. I am the atomic number of carbon. What am I?  

   Answer: 6  

 

  1. I am the gas responsible for global warming. What am I?  

   Answer: Carbon dioxide (CO₂)  

 

  1. I am the process where an acid and a base react to form salt and water. What am I?  

   Answer: Neutralization  

 

  1. I am the process where a solid dissolves in a liquid to form a solution. What am I?  

   Answer: Dissolution  

Difference Between:

  1. Difference between Physical Change and Chemical Change  

   Physical Change: No new substance is formed, and the change is reversible. Example: Melting of ice.  

   Chemical Change: A new substance is formed with different properties, and the change is irreversible. Example: Rusting of iron.  

 

  1. Difference between Element and Compound  

   Element: A pure substance made of only one type of atom. Example: Oxygen (O₂).  

   Compound: A pure substance made of two or more elements chemically combined in a fixed ratio. Example: Water (H₂O).  

 

  1. Difference between Atom and Molecule  

   Atom: The smallest unit of an element that retains its chemical properties. Example: Hydrogen (H).  

   Molecule: A group of two or more atoms chemically bonded together. Example: Oxygen molecule (O₂).  

 

  1. Difference between Molecular Formula and Empirical Formula  

   Molecular Formula: Represents the actual number of atoms of each element in a molecule. Example: C₆H₁₂O₆ (Glucose).  

   Empirical Formula: Represents the simplest whole-number ratio of elements in a compound. Example: CH₂O for glucose.  

 

  1. Difference between Balanced and Unbalanced Chemical Equation  

   Balanced Equation: Has an equal number of atoms of each element on both sides of the equation. Example: 2H₂ + O₂ → 2H₂O.  

   Unbalanced Equation: Does not have an equal number of atoms on both sides. Example: H₂ + O₂ → H₂O.  

 

  1. Difference between Exothermic and Endothermic Reactions  

   Exothermic Reaction: Releases heat energy. Example: Combustion of methane (CH₄ + O₂ → CO₂ + H₂O + Heat).  

   Endothermic Reaction: Absorbs heat energy. Example: Photosynthesis.  

 

  1. Difference between Ionic and Covalent Compounds  

   Ionic Compound: Formed by the transfer of electrons between metals and non-metals. Example: NaCl (Sodium chloride).  

   Covalent Compound: Formed by the sharing of electrons between non-metal atoms. Example: H₂O (Water).  

 

  1. Difference between Acidic Oxides and Basic Oxides  

   Acidic Oxides: Oxides of non-metals that react with water to form acids. Example: CO₂ forms H₂CO₃.  

   Basic Oxides: Oxides of metals that react with water to form bases. Example: Na₂O forms NaOH.  

 

  1. Difference between Homogeneous and Heterogeneous Mixtures  

   Homogeneous Mixture: Uniform composition throughout. Example: Saltwater.  

   Heterogeneous Mixture: Non-uniform composition. Example: Sand and water.  

 

  1. Difference between Metals and Non-Metals  

   Metals: Good conductors of heat and electricity, malleable and ductile. Example: Iron (Fe).  

   Non-Metals: Poor conductors of heat and electricity, brittle. Example: Sulfur (S).  

 

  1. Difference between Molecular Mass and Atomic Mass  

   Molecular Mass: Sum of the atomic masses of all atoms in a molecule. Example: H₂O = (2×1) + (1×16) = 18 u.  

   Atomic Mass: Mass of a single atom of an element. Example: Hydrogen = 1 u.  

 

  1. Difference between Anions and Cations  

   Anions: Negatively charged ions formed by gain of electrons. Example: Cl⁻ (Chloride ion).  

   Cations: Positively charged ions formed by loss of electrons. Example: Na⁺ (Sodium ion).  

 

  1. Difference between Law of Conservation of Mass and Law of Constant Proportion  

   Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.  

   Law of Constant Proportion: A given compound always contains the same elements in the same proportion by mass.  

 

  1. Difference between Decomposition and Combination Reactions  

   Decomposition Reaction: A single compound breaks down into simpler substances. Example: CaCO₃ → CaO + CO₂.  

   Combination Reaction: Two or more substances combine to form a single compound. Example: H₂ + O₂ → H₂O.  

 

  1. Difference between Displacement and Double Displacement Reactions  

   Displacement Reaction: A more reactive element replaces a less reactive element in a compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu.  

   Double Displacement Reaction: Exchange of ions between two compounds. Example: NaCl + AgNO₃ → NaNO₃ + AgCl.  

 

  1. Difference between Molecular Equation and Ionic Equation  

   Molecular Equation: Shows reactants and products in molecular form. Example: NaCl + AgNO₃ → NaNO₃ + AgCl.  

   Ionic Equation: Shows only the ions involved in the reaction. Example: Na⁺ + Cl⁻ + Ag⁺ + NO₃⁻ → AgCl + Na⁺ + NO₃⁻.  

 

  1. Difference between Concentrated and Dilute Solutions  

   Concentrated Solution: Contains a large amount of solute. Example: Strong HCl solution.  

   Dilute Solution: Contains a small amount of solute. Example: Weak HCl solution.  

 

  1. Difference between Strong Acids and Weak Acids  

   Strong Acids: Completely ionize in water. Example: HCl, H₂SO₄.  

   Weak Acids: Partially ionize in water. Example: CH₃COOH (Acetic acid).  

 

  1. Difference between Strong Bases and Weak Bases  

   Strong Bases: Completely dissociate in water. Example: NaOH, KOH.  

   Weak Bases: Partially dissociate in water. Example: NH₄OH (Ammonium hydroxide).  

 

  1. Difference between Oxidation and Reduction  

   Oxidation: Loss of electrons or gain of oxygen. Example: Zn → Zn²⁺ + 2e⁻.  

   Reduction: Gain of electrons or loss of oxygen. Example: Cu²⁺ + 2e⁻ → Cu.  

Assertion and Reason

  1. Assertion (A): A chemical equation must be balanced.  

   Reason (R): The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction.  

   Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): A molecule of oxygen is represented as O₂.  

   Reason (R): Oxygen exists as a monoatomic gas under normal conditions.  

   Answer: (A) is true, but (R) is false.  

 

  1. Assertion (A): CO₂ is a compound.  

   Reason (R): Compounds are formed when two or more elements chemically combine in a fixed ratio.  

   Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): NaCl is a mixture of sodium and chlorine.  

   Reason (R): NaCl is formed by a chemical combination of sodium and chlorine in a fixed proportion.  

   Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): Fe is a compound.  

   Reason (R): A compound contains two or more different types of atoms.  

   Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): H₂O is called a compound.  

   Reason (R): Water contains two hydrogen atoms and one oxygen atom chemically bonded.  

   Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): A catalyst alters the speed of a chemical reaction.  

   Reason (R): A catalyst gets consumed in the reaction.  

   Answer: (A) is true, but (R) is false.  

 

  1. Assertion (A): HCl is an acid.  

   Reason (R): Acids release OH⁻ ions in aqueous solutions.  

   Answer: (A) is true, but (R) is false.  

 

  1. Assertion (A): Rusting of iron occurs faster in humid conditions.  

   Reason (R): The presence of water and oxygen accelerates the oxidation of iron.  

   Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Chemical reactions involve breaking and forming of bonds.  

    Reason (R): Chemical changes result in the formation of new substances.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Water is an element.  

    Reason (R): An element consists of only one type of atom.  

    Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): An ionic bond is formed by the sharing of electrons.  

    Reason (R): Ionic bonds are formed by the complete transfer of electrons.  

    Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): MgO is an acidic oxide.  

    Reason (R): Metal oxides generally form basic solutions in water.  

    Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): All metals react with acids to form hydrogen gas.  

    Reason (R): Gold and platinum react vigorously with acids.  

    Answer: (A) is false, but (R) is also false.  

 

  1. Assertion (A): Noble gases do not form compounds easily.  

    Reason (R): Noble gases have a stable electronic configuration.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Decomposition reactions are always endothermic.  

    Reason (R): Decomposition requires energy input in the form of heat, light, or electricity.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): CO is a highly toxic gas.  

    Reason (R): Carbon monoxide binds strongly with hemoglobin, reducing oxygen transport.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Combustion reactions are exothermic.  

    Reason (R): They release heat and light energy during the reaction.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Hydrogen can be collected over water.  

    Reason (R): Hydrogen is insoluble in water.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): The formula of ammonia is NH₃.  

    Reason (R): Ammonia contains one nitrogen and three hydrogen atoms.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): NaCl conducts electricity in solid state.  

    Reason (R): Ionic compounds conduct electricity only in molten or dissolved state.  

    Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): NH₄Cl is an acidic salt.  

    Reason (R): It is formed from a strong acid and a weak base.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): The molecular formula of glucose is C₆H₁₂O₆.  

    Reason (R): Glucose contains carbon, hydrogen, and oxygen in a fixed ratio.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

 

  1. Assertion (A): Electrolysis of water gives H₂ and O₂ in 1:1 ratio.  

    Reason (R): Water has two hydrogen atoms and one oxygen atom.  

    Answer: (A) is false, but (R) is true.  

 

  1. Assertion (A): Oxygen is necessary for combustion.  

    Reason (R): Oxygen is a supporter of combustion.  

    Answer: (A) and (R) are true, and (R) is the correct explanation of (A).  

True or False

  1. The symbol of sodium is Na.  

   True  

  1. CO₂ is the molecular formula for carbon monoxide.  

   False  

  1. The atomic number of oxygen is 8.  

   True  

  1. A chemical equation must always be balanced.  

   True  

  1. The valency of hydrogen is 2.  

   False  

  1. A catalyst speeds up a chemical reaction without being consumed.  

   True  

  1. NaCl is the chemical formula for calcium chloride.  

   False  

  1. The molecular mass of H₂O is 18 g/mol.  

   True  

  1. Hydrogen gas is denser than oxygen gas.  

   False  

  1. Avogadro’s number is 6.022 × 10²³.  

   True  

  1. The mass of reactants and products must be equal in a chemical reaction.  

   True  

  1. The formula for sulfuric acid is H₂SO₄.  

   True  

  1. HCl is a base.  

   False  

  1. The chemical symbol of iron is Fe.  

   True  

  1. The atomic mass of carbon is 12 amu.  

   True  

  1. NH₃ is the formula for ammonia.  

   True  

  1. The law of conservation of mass states that matter can be created or destroyed.  

   False  

  1. The valency of chlorine is 1.  

   True  

  1. MgO is the formula of magnesium hydroxide.  

   False  

  1. Noble gases have a complete outermost shell of electrons.  

   True  

  1. Ca(OH)₂ is called lime water.  

   True  

  1. The molar mass of CO₂ is 28 g/mol.  

   False  

  1. The formula for methane is CH₄.  

   True  

  1. A decomposition reaction involves the breaking down of a compound.  

   True  

  1. CuSO₄ is copper sulfate.  

   True  

  1. A balanced chemical equation violates the law of conservation of mass.  

   False  

  1. O₂ is the molecular formula for ozone.  

   False  

  1. The pH of a neutral solution is 7.  

   True  

  1. The atomic number of sodium is 12.  

   False  

  1. H₂O₂ is the formula for hydrogen peroxide.  

   True  

  1. The molar mass of NaCl is 58.5 g/mol.  

   True  

  1. The formula for nitric acid is HNO₂.  

   False  

  1. H₂ + O₂ → H₂O is a correctly balanced equation.  

   False  

  1. The charge on a sulfate ion (SO₄) is -2.  

   True  

  1. Hydrogen exists as diatomic molecules.  

   True  

  1. The chemical formula for acetic acid is CH₃COOH.  

   True  

  1. The molecular mass of O₂ is 32 g/mol.  

   True  

  1. In a double displacement reaction, two compounds exchange ions.  

   True  

  1. A covalent bond is formed by the sharing of electrons.  

   True  

  1. The atomic number of helium is 4.  

   False  

  1. The valency of nitrogen is 5.  

   False  

  1. Na₂CO₃ is the formula for sodium carbonate.  

   True  

  1. An endothermic reaction releases heat energy.  

   False  

  1. Metals form negative ions by gaining electrons.  

   False  

  1. Oxygen supports combustion.  

   True  

  1. The empirical formula of benzene (C₆H₆) is CH.  

   True  

  1. Rusting of iron is a physical change.  

   False  

  1. The symbol for silver is Ag.  

   True  

  1. The chemical formula of quicklime is CaO.  

   True  

  1. An acid turns blue litmus red.  

   True  

Long Answer Questions

  1. Explain the Law of Conservation of Mass with an example.  

Answer: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. The total mass of the reactants is always equal to the total mass of the products.  

 Example: In the reaction 2H₂ + O₂ → 2H₂O, the total mass of hydrogen and oxygen before the reaction is equal to the total mass of water produced.  

 

  1. Define valency. How is it determined?  

Answer: Valency is the combining capacity of an atom. It is determined by the number of electrons an atom loses, gains, or shares to complete its octet. For example, sodium (Na) has a valency of 1 as it loses one electron to form Na⁺.  

 

  1. Differentiate between a molecule and a compound with examples.  

Answer:A molecule is formed when two or more atoms combine chemically (O₂, H₂O).  

   A compound consists of molecules made from different elements (H₂O, CO₂).  

 

  1. Explain the significance of a balanced chemical equation.  

Answer: A balanced chemical equation follows the Law of Conservation of Mass. It ensures that the number of atoms of each element remains the same on both sides of the equation, maintaining mass balance in a reaction.  

 

  1. What is a chemical formula? Explain with an example.  

Answer: A chemical formula represents the composition of a molecule using element symbols and numerical subscripts. Example: H₂O represents water, where two hydrogen atoms are bonded to one oxygen atom.  

 

  1. Write a note on molecular and empirical formulas with examples.  

Answer: The molecular formula shows the actual number of atoms in a molecule (C₆H₆ for benzene). The empirical formula represents the simplest ratio (CH for benzene).  

 

  1. What is the difference between an ion and a radical?  

Answer: An ion is a charged particle (Na⁺, Cl⁻), while a radical is a group of atoms carrying a charge (SO₄²⁻, NH₄⁺).  

 

  1. Explain the formation of an ionic bond with an example.  

Answer: An ionic bond forms when one atom transfers electrons to another. Example: NaCl forms when Na donates an electron to Cl, creating Na⁺ and Cl⁻.  

 

  1. Explain the formation of a covalent bond with an example.  

Answer: A covalent bond forms when atoms share electrons. Example: H₂O forms when oxygen shares electrons with two hydrogen atoms.  

 

  1. What is the significance of Avogadro’s number?  

Answer: Avogadro’s number (6.022 × 10²³) represents the number of atoms, ions, or molecules in one mole of a substance, facilitating calculations in chemistry.  

 

  1. Differentiate between physical and chemical changes with examples.  

Answer: Physical changes alter appearance but not composition (melting ice). Chemical changes produce new substances (burning paper).  

 

  1. What are the rules for writing chemical symbols?  

Answer: The first letter is capital (O for oxygen). If there’s a second letter, it is lowercase (Na for sodium).  

 

  1. Write the molecular formulas of:  
  2. a) Ammonia (NH₃)  
  3. b) Glucose (C₆H₁₂O₆)  
  4. c) Sulfuric acid (H₂SO₄)  

 

  1. Explain the difference between exothermic and endothermic reactions with examples.  

   Answer: Exothermic reactions release heat (combustion). Endothermic reactions absorb heat (photosynthesis).  

 

  1. Define oxidation and reduction with an example.  

  Answer: Oxidation is the loss of electrons (Na → Na⁺ + e⁻). Reduction is the gain of electrons (Cl₂ + 2e⁻ → 2Cl⁻).  

 

  1. Explain why noble gases are chemically inert.  

 Answer: Noble gases have a complete outer shell of electrons, making them stable and non-reactive.  

 

  1. What is the valency of elements in group 1 and group 17?  

  Answer: Group 1 elements have a valency of 1 (Na⁺). Group 17 elements also have a valency of 1 (Cl⁻).  

 

  1. Why is a chemical equation balanced?  

Answer: To satisfy the Law of Conservation of Mass, ensuring that the total mass of reactants equals the mass of products.  

 

  1. What are polyatomic ions? Give two examples.  

Answer: Ions composed of multiple atoms. Examples: SO₄²⁻ (sulfate), NH₄⁺ (ammonium).  

 

  1. Write a balanced equation for the reaction of magnesium with hydrochloric acid.  

Answer: Mg + 2HCl → MgCl₂ + H₂  

 

  1. Define atomic number and atomic mass with examples.  

   Answer: The atomic number is the number of protons (oxygen: 8). Atomic mass is the sum of protons and neutrons (oxygen: 16 amu).  

 

  1. Explain the concept of molar mass with an example.  

   Answer: The mass of one mole of a substance (H₂O = 18 g/mol).  

 

  1. What is the difference between reactants and products?  

Answer: Reactants are starting materials (H₂, O₂). Products are the substances formed (H₂O).  

 

  1. Write the balanced equation for the combustion of methane.  

 Answer: CH₄ + 2O₂ → CO₂ + 2H₂O  

 

  1. How is a chemical reaction represented?  

 Answer: Using chemical equations that show reactants, products, and coefficients.  

 

  1. Differentiate between empirical and molecular formulas.  

 Answer: The empirical formula is the simplest ratio (CH for benzene), while the molecular formula gives exact numbers (C₆H₆).  

 

  1. What is a decomposition reaction? Give an example.  

Answer: A reaction where a compound breaks into simpler substances (CaCO₃ → CaO + CO₂).  

 

  1. Explain the role of a catalyst in a chemical reaction.  

 Answer: A catalyst speeds up a reaction without being consumed (MnO₂ in H₂O₂ decomposition).  

 

  1. What are chemical symbols? Give two examples.  

  Answer: Representations of elements (H for hydrogen, O for oxygen).  

 

  1. What are oxidation numbers? Give an example.  

 Answer: The charge an atom appears to have in a compound (O in H₂O = -2).  

 

  1. Write the formulae for the following:  
  2. a) Calcium carbonate (CaCO₃)  
  3. b) Nitric acid (HNO₃)  
  4. c) Magnesium sulfate (MgSO₄)  

 

  1. Why is H₂O called a polar molecule?  

Answer: Due to an unequal sharing of electrons between oxygen and hydrogen.  

 

  1. Define atomic structure.  

 Answer: The arrangement of protons, neutrons, and electrons in an atom.  

 

  1. What is meant by molarity?  

Answer: The number of moles of solute per liter of solution.  

 

  1. Write the balanced equation for photosynthesis.  

Answer: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂  

 

  1. What are isotopes? Give an example.  

Answer: Atoms of the same element with different neutron numbers (C-12, C-14).  

 

  1. Explain the octet rule with an example.  

Answer: Atoms tend to have eight electrons in their valence shell (Ne).  

 

  1. What are the products of electrolysis of water?  

Answer: Hydrogen and oxygen gases.  

 

  1. Define an empirical formula with an example.  

Answer: The simplest ratio of atoms (CH₂ for ethene).  

 

  1. What is the role of valency in chemical bonding?  

Answer: Determines how elements combine to form compounds.  

 

  1. Explain the process of rusting.  

 Answer: Iron reacts with oxygen and water to form Fe₂O₃·xH₂O.  

 

  1. Write the balanced equation for the reaction of aluminum with oxygen.  

Answer: 4Al + 3O₂ → 2Al₂O₃  

 

  1. What is a molecular ion?  

Answer: A charged molecule (NH₄⁺).  

 

  1. How does CO₂ contribute to global warming?  

Answer: Traps heat in the atmosphere, causing temperature rise.  

 

  1. What are electrolytes? Give an example.  

   Answer: Substances that conduct electricity in solution (NaCl).  

 

  1. What is a combustion reaction?  

Answer: A reaction in which a substance burns in oxygen to release energy.  

 

  1. Write the formula for plaster of Paris.  

Answer: CaSO₄·½H₂O  

 

  1. How do acids react with metals?  

Answer: They release hydrogen gas (Zn + 2HCl → ZnCl₂ + H₂).  

 

  1. Write the reaction for the neutralization of NaOH with HCl.  

Answer: NaOH + HCl → NaCl + H₂O  

 

  1. What are noble gases?  

  Answer: Elements in Group 18 that are chemically inert.  

Give Reasons

  1. Why is the Law of Conservation of Mass important in chemistry?  

  Answer: It ensures that the total mass of reactants and products remains equal, maintaining mass balance in reactions.  

 

  1. Why do noble gases not form compounds easily?  

   Answer: They have a complete outermost shell of electrons, making them chemically inert.  

 

  1. Why is a chemical equation balanced?  

Answer: To satisfy the Law of Conservation of Mass and ensure the number of atoms remains equal on both sides.  

 

  1. Why is water a universal solvent?  

  Answer: Because it can dissolve many substances due to its polarity and hydrogen bonding.  

 

  1. Why do metals lose electrons to form positive ions?  

Answer: Metals have low ionization energy and tend to achieve noble gas configuration by losing electrons.  

 

  1. Why does hydrogen form both covalent and ionic bonds?  

  Answer: Hydrogen can either share an electron (covalent bond) or lose/gain an electron (ionic bond).  

 

  1. Why is HCl a strong acid?  

Answer: It completely ionizes in water to release H⁺ ions.  

 

  1. Why does rusting of iron take place faster in coastal areas?  

 Answer: High moisture and salt in the air accelerate the oxidation process.  

 

  1. Why does burning of coal release carbon dioxide?  

Answer: Coal is mainly carbon, and it reacts with oxygen to form CO₂ during combustion.  

 

  1. Why is diamond harder than graphite?  

 Answer: Diamond has a strong 3D tetrahedral structure, while graphite has weak interlayer forces.  

 

  1. Why does sodium react vigorously with water?  

Answer: Sodium is highly reactive and reacts exothermically with water, releasing hydrogen gas.  

 

  1. Why does copper not react with dilute HCl?  

   Answer: Copper is below hydrogen in the reactivity series and cannot displace hydrogen from acids.  

 

  1. Why does an ionic compound conduct electricity in a solution but not in solid form?  

   Answer: In solution, ions are free to move, while in solid form, they are fixed in a lattice.  

 

  1. Why is graphite a good conductor of electricity?  

  Answer: It has free-moving delocalized electrons between layers.  

 

  1. Why is ammonia soluble in water?  

  Answer: Ammonia forms hydrogen bonds with water molecules.  

 

  1. Why does an iron nail sink in water but a ship floats?  

   Answer: The ship’s shape increases buoyancy, whereas the nail has high density and displaces less water.  

 

  1. Why is silver used for making ornaments?  

   Answer: It is lustrous, malleable, and resistant to corrosion.  

 

  1. Why does the color of copper sulfate solution change when iron is added?  

  Answer: Iron displaces copper from the solution due to higher reactivity.  

 

  1. Why does ice float on water?  

Answer: Ice is less dense than liquid water due to its open lattice structure.  

 

  1. Why does food cook faster in a pressure cooker?  

Answer: High pressure increases the boiling point of water, allowing food to cook at a higher temperature.  

 

  1. Why does salt dissolve in water but not in oil?  

   Answer: Salt is ionic and dissolves in polar solvents like water, while oil is non-polar.  

 

  1. Why do acids turn blue litmus paper red?  

 Answer: Acids release H⁺ ions in solution, which react with the indicator to change its color.  

 

  1. Why do alkali metals have low melting points?  

 Answer: They have weak metallic bonds due to a single valence electron.  

 

  1. Why does limewater turn milky when CO₂ is passed through it?  

  Answer: CO₂ reacts with Ca(OH)₂ to form insoluble calcium carbonate.  

 

  1. Why do atoms form chemical bonds?  

Answer: To attain stability by completing their octet or duplet.  

 

  1. Why is carbon dioxide used in fire extinguishers?  

 Answer: It is heavier than air and forms a blanket over the fire, cutting off oxygen supply.  

 

  1. Why does ethanol evaporate faster than water?  

Answer: It has weaker intermolecular forces compared to water.  

 

  1. Why is NaCl neutral in nature?  

  Answer:  It is formed from a strong acid (HCl) and a strong base (NaOH), resulting in a neutral solution.  

 

  1. Why does chlorine have a higher electronegativity than sodium?  

Answer: Chlorine has more protons and a smaller atomic radius, attracting electrons more strongly.  

 

  1. Why do noble gases have low boiling points?  

Answer: They exist as monoatomic gases with weak van der Waals forces.  

 

  1. Why is baking soda used in baking?  

Answer: It releases CO₂ gas, making the dough rise and become fluffy.  

 

  1. Why do we see bubbles when zinc reacts with hydrochloric acid?  

Answer: Hydrogen gas is released during the reaction.  

 

  1. Why do diamonds sparkle?  

  Answer: Due to total internal reflection of light.  

 

  1. Why is gold preferred for making coins and jewelry?  

Answer: It is non-reactive, malleable, and has a bright luster.  

 

  1. Why does sugar not conduct electricity in water?  

Answer: It does not dissociate into ions in solution.  

 

  1. Why does milk turn sour when kept for a long time?  

Answer: Bacteria convert lactose into lactic acid, making it acidic.  

 

  1. Why does an increase in temperature speed up a chemical reaction?  

Answer: It increases the kinetic energy of molecules, leading to more collisions.  

 

  1. Why does adding salt to ice lower its melting point?  

   – Salt disrupts the formation of the ice lattice, causing it to melt at a lower temperature.  

 

  1. Why do helium balloons rise in the air?  

Answer: Helium is lighter than air, causing buoyancy.  

 

  1. Why does the rate of evaporation increase with wind speed?  

Answer: Moving air carries away water vapor, allowing more liquid to evaporate.  

 

  1. Why is distilled water a poor conductor of electricity?  

Answer: It lacks free ions to conduct electricity.  

 

  1. Why is dry hydrogen gas collected over water?  

Answer: It is insoluble in water and lighter than air.  

 

  1. Why does iron become brittle when exposed to moisture?  

Answer: Rusting weakens the iron structure.  

 

  1. Why do ionic compounds have high melting points?  

Answer: They have strong electrostatic forces of attraction between ions.  

 

  1. Why does sodium hydroxide feel slippery?  

Answer: It reacts with skin oils to form soap-like compounds.  

 

  1. Why does H₂SO₄ have a higher boiling point than HCl?  

Answer: H₂SO₄ has stronger hydrogen bonding and higher molecular mass.  

 

  1. Why does charcoal absorb gases?  

Answer: It has a highly porous structure that traps gas molecules.  

 

  1. Why do acids react with carbonates to produce bubbles?  

Answer: Acids react with carbonates to form CO₂ gas.  

 

  1. Why does bleaching powder lose its effectiveness over time?  

Answer: It decomposes when exposed to air and moisture.  

 

  1. Why does cooking oil not mix with water?  

Answer: Oil is non-polar, and water is polar, so they do not dissolve in each other.  

Arrange the Words 

Case Studies

  1. Case Study:  

   Rohan was experimenting in the lab and heated a mixture of iron filings and sulfur. He noticed that a black solid was formed, which was not magnetic. He was confused if a physical or chemical change had taken place.  

   Question: What type of change occurred, and why?  

   Answer: A chemical change occurred because iron and sulfur combined to form iron sulfide (FeS), a new substance with different properties.

  1. Case Study:  

   Priya observed that when she left an iron nail in copper sulfate solution, the blue color faded, and a reddish-brown deposit formed on the nail.  

   Question: Identify the reaction and explain.  

     Answer: This is a displacement reaction where iron (Fe) displaces copper (Cu) from copper sulfate solution:  

   Fe + CuSO₄ → FeSO₄ + Cu.

  1. Case Study:  

   A student mixed hydrochloric acid (HCl) with sodium hydroxide (NaOH) in a beaker and noticed that the temperature of the solution increased.  

   Question: What type of reaction is this?  

     Answer: This is a neutralization reaction, and it is exothermic as it releases heat:  

   HCl + NaOH → NaCl + H₂O + Heat.

  1. Case Study:  

   A chemist heated a green-colored solid in a test tube and observed the release of a colorless gas with a pungent smell. The solid changed color to black.  

   Question: Identify the reaction and the substances involved.  

     Answer: This is the thermal decomposition of copper carbonate:  

   CuCO₃ → CuO + CO₂.

  1. Case Study:  

   Raj boiled water in a kettle and observed that white deposits formed on the inner walls of the kettle.  

   Question: What caused this deposition?  

     Answer: The white deposits are due to the precipitation of calcium and magnesium salts from hard water.

  1. Case Study:  

   A piece of marble was placed in a beaker containing dilute hydrochloric acid, and bubbles were observed.  

   Question: Write the chemical reaction involved.  

     Answer: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O.

  1. Case Study:  

   Sunil noticed that milk left outside for a day turned sour.  

   Question: What type of change is this?  

     Answer: This is a chemical change due to lactic acid formation caused by bacterial fermentation.

  1. Case Study:  

   A student added barium chloride to sodium sulfate solution and observed a white precipitate.  

   Question: Write the reaction.  

     Answer: BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl.

  1. Case Study:  

   Vinegar was added to baking soda, and fizzing was observed.  

   Question: What gas is released in this reaction?  

     Answer: Carbon dioxide (CO₂) is released:  

   CH₃COOH + NaHCO₃ → CO₂ + H₂O + NaCH₃COO.

  1. Case Study:  

   A black residue was left behind when sugar was heated strongly in a test tube.  

   Question: Explain the observation.  

     Answer: Sugar (C₆H₁₂O₆) undergoes thermal decomposition, leaving behind carbon (C) and water vapor.

  1. Case Study:  

   When hydrogen peroxide was stored in a clear bottle, bubbles formed over time.  

   Question: What caused this?  

     Answer: Hydrogen peroxide decomposes in light, releasing oxygen:  

   2H₂O₂ → 2H₂O + O₂.

  1. Case Study:  

   During a chemical experiment, a student observed that a substance absorbed water vapor from the air and turned into a liquid.  

   Question: What is this process called?  

     Answer: This is deliquescence.

  1. Case Study:  

   A silver spoon turned black when left in the open air for several days.  

   Question: What caused this?  

     Answer: Silver reacts with hydrogen sulfide (H₂S) in the air, forming black silver sulfide (Ag₂S).

  1. Case Study:  

   A gas was passed through limewater, turning it milky.  

   Question: Identify the gas.  

     Answer: The gas is carbon dioxide (CO₂).

  1. Case Study:  

   A student noticed that a gas with a rotten egg smell was released when dilute HCl was added to an unknown solid.  

   Question: Identify the gas.  

     Answer: The gas is hydrogen sulfide (H₂S).

  1. Case Study:  

   A copper vessel used for storing food turned green over time.  

   Question: What caused this?  

     Answer: Copper reacts with air and moisture to form a green patina of copper carbonate.

  1. Case Study:  

   A white powder was strongly heated, and it turned yellow when hot but became white again when cooled.  

   Question: Identify the substance.  

     Answer: The substance is zinc oxide (ZnO).

  1. Case Study:  

   A reaction produced a lot of heat and light and was used in welding.  

   Question: Identify the reaction.  

     Answer: This is the thermite reaction:  

   Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + Heat.

  1. Case Study:  

   A reddish-brown metal was left in air and developed a greenish layer over time.  

   Question: Name the metal and the compound formed.  

     Answer: The metal is copper (Cu), and the compound formed is copper carbonate (CuCO₃).

  1. Case Study:  

   A student added ammonium hydroxide to iron (III) chloride solution and observed a brown precipitate.  

   Question: Identify the precipitate.  

     Answer: The precipitate is ferric hydroxide (Fe(OH)₃).  

Numericals

Numeric problems are not available for this chapter.

ICSE Grade 9

3500/-
  • All Subjects
  • Free Study Material
  • MCQ Tests
  • Theory Tests
  • Assignments
Register

Find out free resources that you need.

ICSE

Grade 8

Grade 9

Grade 10

CBSE

Grade 8

Grade 9

Grade 10

Subjects we teach

“Arise, awake, and learn by approaching the excellent teachers”

Shiksha Marg 108 gives you all free resources to ensure you get the best results. Get ready for you ICSE and CBSE exams!.

ENROLL
ENROLL
error:
Scroll to Top