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Class 10 Science: Chemical Reactions and Equations, 8 practice questions with answers

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These are 8 practice questions on NCERT Class 10 Science Chapter 1, Chemical Reactions and Equations, each with a short answer and the textbook page it comes from. They cover balancing equations, the types of reaction (combination, decomposition, displacement), exothermic and endothermic reactions, oxidation and reduction, and one numerical on masses. Try each one before you read the answer. The ideas behind each step are in our guide to NCERT Class 10 Science Chapter 1, Chemical Reactions and Equations.

These questions are our own, drafted with AI help. Every number was re-computed by a test script and every statement was checked against the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Science, Textbook for Class X, Reprint 2026-27, Chapter 1, printed pages 1 to 16):

Balancing equations

Question 1. Balance the equation Mg + O₂ → MgO using the smallest whole-number coefficients. What is the sum of all the coefficients in the balanced equation?

Answer: 5. Balanced: 2Mg + O₂ → 2MgO, with 2 Mg atoms and 2 O atoms on each side. The sum of the coefficients is 2 + 1 + 2 = 5. (Page 3.)

Question 2. Balance N₂ + H₂ → NH₃ using the smallest whole numbers. What is the sum of the coefficients?

Answer: 6. N₂ + 3H₂ → 2NH₃ has 2 N atoms and 6 H atoms on each side, so the coefficients are 1, 3 and 2, and their sum is 1 + 3 + 2 = 6. (The rule is the balancing rule on page 3.)

Question 3. Aluminium burns in oxygen to form aluminium oxide: Al + O₂ → Al₂O₃. (a) Balance the equation with the smallest whole numbers. (b) In one experiment, 108 g of aluminium burns completely in 96 g of oxygen and nothing is left over. What mass of aluminium oxide forms, in grams?

Answer: (a) 4Al + 3O₂ → 2Al₂O₃. (b) Mass can neither be created nor destroyed in a chemical reaction (page 3), so the mass of the product equals the mass of the reactants: 108 + 96 = 204 g of aluminium oxide.

Types of reaction

Question 4. Quick lime reacts with water: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat. This reaction is best described as: (a) a combination reaction that is exothermic; (b) a decomposition reaction that is endothermic; (c) a displacement reaction that is exothermic; or (d) a double displacement reaction that is endothermic.

Answer: (a), a combination reaction that is exothermic. Two reactants form a single product, so it is a combination reaction; heat is released, so it is exothermic. (Pages 6 and 7.)

Question 5. Assertion (A): Decomposition reactions are generally endothermic. Reason (R): To break the reactant apart, energy has to be supplied as heat, light or electricity. Choose the correct option: both true and R explains A; both true but R does not explain A; A true and R false; or A false and R true.

Answer: A and R are both true, and R explains A. Decomposition needs heat (for example heating ferrous sulphate), light (silver chloride turns grey in sunlight) or electricity (water). Reactions that absorb energy are endothermic. (Pages 8 to 10.)

Question 6. Which statement correctly explains what happens when an iron nail is kept in copper sulphate solution for some time? (Copper displaces iron from the nail, forming copper oxide; the nail only rusts and the solution takes no part in any reaction; or iron displaces copper from copper sulphate, forming iron sulphate and copper.)

Answer: iron displaces copper from copper sulphate, forming iron sulphate and copper. Fe + CuSO₄ → FeSO₄ + Cu is a displacement reaction: the nail turns brownish and the blue colour of the solution fades. (Page 11.)

Question 7. Zinc is added to copper sulphate solution: Zn + CuSO₄ → ZnSO₄ + Cu. What type of reaction is this, and which metal is more reactive, zinc or copper?

Answer: a displacement reaction; zinc is more reactive. Zinc displaces copper from its compound; the textbook notes that zinc and lead are more reactive than copper and displace copper from its compounds. (Page 11.)

Oxidation and reduction

Question 8. In the reaction ZnO + C → Zn + CO, which substance is reduced?

Answer: ZnO is reduced; carbon is oxidised. ZnO loses oxygen and becomes Zn, so it is reduced; carbon gains oxygen and becomes CO, so it is oxidised. This is a redox reaction. (The textbook gives this reaction as an example of a redox reaction, page 12, and states that carbon is oxidised to CO and ZnO is reduced to Zn, page 13.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook.

The definitions and examples are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.