Class 10 Science – Chapter 1: Chemical Reactions and Equations
1. What happens when magnesium ribbon is burnt in air?
Ans. A. It burns with a dazzling white flame
Magnesium reacts with oxygen in the air to form magnesium oxide and emits white light.
2. Which of the following is a displacement reaction?
Ans. B. Zn + H₂SO₄ → ZnSO₄ + H₂
Here, zinc displaces hydrogen from sulphuric acid, hence a displacement reaction.
3. Which gas is evolved when zinc reacts with dilute hydrochloric acid?
Ans. C. Hydrogen
Zn + 2HCl → ZnCl₂ + H₂↑
4. Which of the following statements about the reaction below are correct?
2PbO(s) + C(s) → 2Pb(s) + CO₂(g)
Ans. B & D
Carbon is oxidised to CO₂, and PbO is reduced to Pb.
6. Which of the following is an endothermic reaction?
Ans. C. Decomposition of calcium carbonate
This reaction requires heat, hence it is endothermic.
7. The chemical formula of quicklime is:
Ans. B. CaO
Quicklime is chemically calcium oxide.
8. A solution of a substance ‘X’ is used for whitewashing. The substance ‘X’ is:
Ans. B. Ca(OH)₂
Slaked lime is used for whitewashing.
9. In which of the following reactions, a brown coating is formed on iron?
Ans. C. Rusting
Rusting of iron produces a brown flaky substance called rust (Fe₂O₃.xH₂O).
10. Which of the following is a displacement reaction?
Ans. C. Zn + CuSO₄ → ZnSO₄ + Cu
It is a classic example of displacement reaction.
11. Which among the following is a redox reaction?
Ans. C. Both A and B
Both reactions involve oxidation and reduction.
12. What happens when iron nails are placed in copper sulphate solution?
Ans. C. Copper gets deposited on iron
Iron displaces copper from the solution.
13. Which gas is evolved when dilute hydrochloric acid reacts with zinc?
Ans. B. Hydrogen
The reaction produces hydrogen gas.
14. The reaction: AgNO₃ + NaCl → AgCl + NaNO₃ is a:
Ans. D. Double displacement
Two compounds exchange ions.
15. The colour of copper sulphate solution is:
Ans. B. Blue
The blue colour is due to hydrated copper ions.
16. Which of the following is a displacement reaction?
Ans. A. Zn + H₂SO₄ → ZnSO₄ + H₂ (Displacement reaction)
17. What type of chemical reaction takes place when quicklime is added to water?
Ans. A. Combination (CaO + H₂O → Ca(OH)₂)
18. The brown coating on iron nails dipped in copper sulphate solution is due to:
Ans. B. Copper (displacement of Cu by Fe)
19. Which of the following is not a chemical change?
Ans. B. Boiling of water (It is a physical change)
20. The chemical reaction involved in the corrosion of iron is:
Ans. C. Oxidation (Iron gets oxidized to form rust)
21. Which of the following is an endothermic reaction?
Ans. B. Decomposition of calcium carbonate (CaCO₃ → CaO + CO₂)
22. What is observed when a piece of iron is placed in copper sulphate solution?
Ans. B. Blue color fades and reddish-brown coating forms (displacement)
23. The reaction of calcium with water is:
Ans. C. Violent and exothermic (Ca + 2H₂O → Ca(OH)₂ + H₂ + heat)
24. Photosynthesis is an example of:
Ans. D. Both B and C (CO₂ + H₂O + sunlight → C₆H₁₂O₆ + O₂)
25. Which of the following is not a characteristic of a chemical reaction?
Ans. D. Melting of ice (It is a physical change)
26. Decomposition of water into hydrogen and oxygen is caused by:
Ans. C. Electric current (electrolysis)
27. Which of the following is used to prevent rancidity in food?
Ans. D. All of the above
28. What is formed when silver chloride is exposed to sunlight?
Ans. A. Silver and chlorine (photodecomposition)
29. The chemical reaction involved in the digestion of food is:
Ans. C. Decomposition (complex food molecules → simpler ones)
30. A chemical equation is balanced to satisfy which law?
Ans. B. Law of conservation of mass
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