⚗️ Chemical Reactions and Equations – Class 10 Science MCQs

Part 1: Basics of Chemical Reactions & Writing Balanced Equations (Q1–Q25)

Q1. Which of the following is a chemical reaction?

A. Melting of ice
B. Rusting of iron
C. Boiling of water
D. Breaking of glass

✅ Correct Answer: B. Rusting of iron

Explanation:

• A, C, D: Physical changes, no new substance formed.
• B: Rusting produces hydrated ferric oxide (new substance) → chemical change.

Q2. Which of the following represents a balanced chemical equation?

A. H₂ + O₂ → H₂O
B. 2H₂ + O₂ → 2H₂O
C. H₂ + O₂ → 2H₂O
D. 2H₂ + O₂ → H₂O

✅ Correct Answer: B. 2H₂ + O₂ → 2H₂O

Q3. The number of atoms of each element must be the same on both sides of an equation to satisfy:

A. Law of gravitation
B. Law of constant proportion
C. Law of conservation of mass
D. Avogadro’s law

✅ Correct Answer: C. Law of conservation of mass

Q4. Which is NOT a characteristic of a chemical reaction?

A. Evolution of gas
B. Formation of precipitate
C. Change in state
D. Increase in weight of reactants

✅ Correct Answer: D. Increase in weight of reactants

Q5. Which reaction is represented by: CaCO₃ → CaO + CO₂?

A. Combination
B. Decomposition
C. Displacement
D. Double displacement

✅ Correct Answer: B. Decomposition

Q6. The reaction: 2Mg + O₂ → 2MgO is a/an:

A. Combination reaction
B. Decomposition reaction
C. Displacement reaction
D. Neutralization

✅ Correct Answer: A. Combination reaction

Q7. In the equation: Zn + 2HCl → ZnCl₂ + H₂, which element is displaced?

A. Zinc
B. Hydrogen
C. Chlorine
D. Oxygen

✅ Correct Answer: B. Hydrogen

Q8. What is the product formed when Fe reacts with CuSO₄?

A. FeSO₄ + Cu
B. CuFe + SO₄
C. FeCu + SO₄
D. Fe₂(SO₄)₃ + Cu

✅ Correct Answer: A. FeSO₄ + Cu

Q9. Which of the following is NOT a physical change?

A. Dissolution of salt in water
B. Freezing of water
C. Burning of paper
D. Sublimation of iodine

✅ Correct Answer: C. Burning of paper

Q10. Which observation indicates a chemical change?

A. Formation of bubbles
B. Change in colour
C. Emission of light or heat
D. All of these

✅ Correct Answer: D. All of these

Q11. Which of the following has NOT undergone a chemical reaction?

A. Cooking of food
B. Ripening of fruit
C. Digestion of food
D. Breaking of glass tumbler

✅ Correct Answer: D. Breaking of glass tumbler

Q12. The reaction: 2KClO₃ → 2KCl + 3O₂ is an example of:

A. Combination
B. Displacement
C. Decomposition
D. Neutralization

✅ Correct Answer: C. Decomposition

Q13. Which type of chemical reaction produces insoluble salts as products?

A. Neutralization
B. Combination
C. Precipitation
D. Displacement

✅ Correct Answer: C. Precipitation

Q14. When silver nitrate solution is mixed with sodium chloride solution, a white precipitate is formed. The reaction is:

A. Combination
B. Double displacement
C. Decomposition
D. Displacement

✅ Correct Answer: B. Double displacement

Q15. The balanced form of Fe + H₂O → Fe₃O₄ + H₂ is:

A. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
B. 3Fe + 4H₂O → Fe₃O₄ + 2H₂
C. 3Fe + 2H₂O → Fe₃O₄ + H₂
D. Fe + 2H₂O → Fe₃O₄ + H₂

✅ Correct Answer: A. 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Q16. Which is a redox reaction?

A. 2Mg + O₂ → 2MgO
B. Zn + CuSO₄ → ZnSO₄ + Cu
C. Both A and B
D. None

✅ Correct Answer: C. Both A and B

Q17. When a chemical equation is balanced, it obeys:

A. Law of conservation of momentum
B. Law of conservation of mass
C. Newton’s laws
D. Boyle’s law

✅ Correct Answer: B. Law of conservation of mass

Q18. Which of the following is endothermic?

A. Burning of wood
B. Respiration
C. Decomposition of CaCO₃
D. Combustion of methane

✅ Correct Answer: C. Decomposition of CaCO₃

Q19. The products of neutralization reaction are:

A. Salt + acid
B. Salt + base
C. Salt + water
D. Acid + base

✅ Correct Answer: C. Salt + water

Q20. Which reaction is represented by: AgNO₃ + NaCl → AgCl + NaNO₃?

A. Displacement
B. Double displacement
C. Combination
D. Decomposition

✅ Correct Answer: B. Double displacement

Q21. Which statement is true about rusting of iron?

A. Only water is required
B. Only oxygen is required
C. Both water and oxygen are required
D. Neither water nor oxygen is required

✅ Correct Answer: C. Both water and oxygen are required

Q22. The equation CH₄ + 2O₂ → CO₂ + 2H₂O is an example of:

A. Decomposition
B. Displacement
C. Combustion
D. Neutralization

✅ Correct Answer: C. Combustion

Q23. Which chemical reaction is used in black and white photography?

A. Decomposition of silver bromide
B. Reaction of NaCl with AgNO₃
C. Burning of magnesium ribbon
D. Photosynthesis

✅ Correct Answer: A. Decomposition of silver bromide

Q24. What happens when magnesium ribbon is burnt in air?

A. It forms MgCl₂
B. It forms MgO (white ash)
C. It forms MgSO₄
D. It forms Mg(OH)₂

✅ Correct Answer: B. It forms MgO (white ash)

Q25. The chemical equation: Pb(NO₃)₂ → PbO + NO₂ + O₂ is an example of:

A. Combination
B. Displacement
C. Double displacement
D. Thermal decomposition

✅ Correct Answer: D. Thermal decomposition

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