Top 50 Most Important MCQs with Answers on Chemical Reactions and Equations
1. A chemical equation which represents the actual masses of reactants and products is called
A) Word equation
B) Skeleton equation
C) Balanced chemical equation
D) Chemical formula
Answer: Balanced chemical equation
2. Which law is followed by a balanced chemical equation?
A) Law of multiple proportions
B) Law of constant proportions
C) Law of conservation of mass
D) Law of gaseous volumes
Answer: Law of conservation of mass
3. Which of the following is a combination reaction?
A) Zn + H₂SO₄ → ZnSO₄ + H₂
B) CaO + H₂O → Ca(OH)₂
C) NaOH + HCl → NaCl + H₂O
D) Fe + CuSO₄ → FeSO₄ + Cu
Answer: CaO + H₂O → Ca(OH)₂
4. Burning of magnesium in air is an example of
A) Decomposition reaction
B) Displacement reaction
C) Combination reaction
D) Double displacement reaction
Answer: Combination reaction
5. Which of the following is a decomposition reaction?
A) CaCO₃ → CaO + CO₂
B) Zn + CuSO₄ → ZnSO₄ + Cu
C) NaOH + HCl → NaCl + H₂O
D) C + O₂ → CO₂
Answer: CaCO₃ → CaO + CO₂
6. Which gas is evolved when zinc reacts with dilute hydrochloric acid?
A) Oxygen
B) Nitrogen
C) Hydrogen
D) Carbon dioxide
Answer: Hydrogen
7. The reaction Fe + CuSO₄ → FeSO₄ + Cu is a
A) Combination reaction
B) Displacement reaction
C) Decomposition reaction
D) Neutralisation reaction
Answer: Displacement reaction
8. Rusting of iron is an example of
A) Oxidation
B) Reduction
C) Both oxidation and reduction
D) Displacement
Answer: Both oxidation and reduction
9. Which substance is oxidised in the reaction Zn + CuSO₄ → ZnSO₄ + Cu?
A) Zinc
B) Copper
C) Copper sulphate
D) Zinc sulphate
Answer: Zinc
10. Which substance is reduced in the same reaction?
A) Zinc
B) Copper
C) Copper sulphate
D) Zinc sulphate
Answer: Copper
11. A reaction in which heat is released is called
A) Endothermic reaction
B) Exothermic reaction
C) Decomposition reaction
D) Displacement reaction
Answer: Exothermic reaction
12. Which of the following reactions is endothermic?
A) Burning of coal
B) Photosynthesis
C) Respiration
D) Rusting
Answer: Photosynthesis
13. Which of the following prevents rusting?
A) Painting
B) Greasing
C) Galvanisation
D) All of these
Answer: Painting, greasing and galvanisation
14. Galvanisation is a process of coating iron with
A) Copper
B) Zinc
C) Tin
D) Silver
Answer: Zinc
15. The chemical formula of rust is
A) FeO
B) Fe₂O₃
C) Fe₂O₃·xH₂O
D) Fe₃O₄
Answer: Fe₂O₃·xH₂O
16. Which type of reaction occurs in electrolysis of water?
A) Combination
B) Decomposition
C) Displacement
D) Double displacement
Answer: Decomposition reaction
17. In a double displacement reaction
A) Atoms are exchanged
B) Molecules are exchanged
C) Ions are exchanged
D) Electrons are exchanged
Answer: Ions are exchanged
18. Which of the following is a double displacement reaction?
A) AgNO₃ + NaCl → AgCl + NaNO₃
B) C + O₂ → CO₂
C) CaO + H₂O → Ca(OH)₂
D) Zn + CuSO₄ → ZnSO₄ + Cu
Answer: AgNO₃ + NaCl → AgCl + NaNO₃
19. Precipitation reactions are
A) Combination reactions
B) Double displacement reactions
C) Decomposition reactions
D) Oxidation reactions
Answer: Double displacement reactions
20. Which of the following is an example of oxidation?
A) Gain of electrons
B) Loss of oxygen
C) Loss of hydrogen
D) Gain of hydrogen
Answer: Loss of hydrogen
21. Which of the following is reduction?
A) Loss of electrons
B) Gain of electrons
C) Gain of oxygen
D) Loss of hydrogen
Answer: Gain of electrons
22. In photosynthesis, carbon dioxide is
A) Oxidised
B) Reduced
C) Neutralised
D) Displaced
Answer: Reduced
23. In respiration, glucose is
A) Reduced
B) Oxidised
C) Displaced
D) Neutralised
Answer: Oxidised
24. Which is a physical change?
A) Rusting of iron
B) Burning of candle
C) Melting of ice
D) Cooking of food
Answer: Melting of ice
25. Which is a chemical change?
A) Boiling of water
B) Cutting of paper
C) Rusting of iron
D) Freezing of water
Answer: Rusting of iron
26. What is a balanced chemical equation?
A) Equal number of molecules
B) Equal number of atoms on both sides
C) Equal mass of substances
D) Equal volume of gases
Answer: Equal number of atoms on both sides
27. Which reagent is used to test carbon dioxide gas?
A) Lime water
B) Blue litmus
C) Phenolphthalein
D) Alcohol
Answer: Lime water
28. Which gas turns lime water milky?
A) Oxygen
B) Carbon dioxide
C) Hydrogen
D) Nitrogen
Answer: Carbon dioxide
29. Which of the following is a redox reaction?
A) Only oxidation
B) Only reduction
C) Both oxidation and reduction
D) Neutralisation
Answer: Both oxidation and reduction
30. Which of the following is not a chemical reaction?
A) Burning of LPG
B) Rusting of iron
C) Melting of wax
D) Digestion of food
Answer: Melting of wax
31. What is corrosion?
A) Formation of oxide layer
B) Destruction of metals by air and moisture
C) Burning of metals
D) Coating of metals
Answer: Destruction of metals by air and moisture
32. Which metal does not corrode easily?
A) Iron
B) Aluminium
C) Silver
D) Gold
Answer: Gold
33. Which reaction produces a precipitate?
A) AgNO₃ + NaCl → AgCl + NaNO₃
B) C + O₂ → CO₂
C) NaOH + HCl → NaCl + H₂O
D) CaO + H₂O → Ca(OH)₂
Answer: AgNO₃ + NaCl → AgCl + NaNO₃
34. What is rancidity?
A) Rusting of iron
B) Oxidation of oils and fats
C) Spoiling of milk
D) Fermentation
Answer: Oxidation of oils and fats
35. Rancidity can be prevented by
A) Heating
B) Adding preservatives
C) Nitrogen flushing
D) All of these
Answer: Heating, adding preservatives and nitrogen flushing
36. Which substance acts as an oxidising agent?
A) A substance that gets oxidised
B) A substance that gets reduced
C) A substance that loses electrons
D) A substance that gains hydrogen
Answer: A substance that gets reduced
37. Which one is a reducing agent?
A) A substance that gets oxidised
B) A substance that gets reduced
C) A substance that gains electrons
D) A substance that gains oxygen
Answer: A substance that gets oxidised
38. Which of the following is a correct balanced chemical equation?
A) H₂ + O₂ → H₂O
B) H₂ + O₂ → 2H₂O
C) 2H₂ + O₂ → 2H₂O
D) H₂ + 2O₂ → 2H₂O
Answer: 2H₂ + O₂ → 2H₂O
39. In the reaction 2H₂ + O₂ → 2H₂O, hydrogen is
A) Oxidised
B) Reduced
C) Neither oxidised nor reduced
D) Neutral
Answer: Oxidised
40. In the same reaction, oxygen is
A) Oxidised
B) Reduced
C) Neutral
D) Displaced
Answer: Reduced
41. Which type of reaction takes place in an electric battery?
A) Combination reaction
B) Redox reaction
C) Decomposition reaction
D) Neutralisation reaction
Answer: Redox reaction
42. Which reaction represents thermal decomposition of limestone?
A) CaCO₃ → CaO + CO₂
B) CaO + CO₂ → CaCO₃
C) CaCO₃ → Ca + CO₃
D) CaO + H₂O → Ca(OH)₂
Answer: CaCO₃ → CaO + CO₂
43. Which of the following is a neutralisation reaction?
A) HCl + NaOH → NaCl + H₂O
B) C + O₂ → CO₂
C) CaO + H₂O → Ca(OH)₂
D) Fe + CuSO₄ → FeSO₄ + Cu
Answer: HCl + NaOH → NaCl + H₂O
44. What happens when copper is heated in air?
A) It turns green
B) It forms black copper oxide
C) It melts
D) It evaporates
Answer: It forms black copper oxide
45. Which of the following indicates a chemical reaction?
A) Change in size
B) Change in state
C) Formation of gas
D) Change in shape
Answer: Formation of gas
46. Which of the following is not a type of chemical reaction?
A) Combination
B) Decomposition
C) Evaporation
D) Displacement
Answer: Evaporation
47. Which metal is used to prevent rusting of iron?
A) Copper
B) Zinc
C) Silver
D) Aluminium
Answer: Zinc
48. Which gas is filled in food packets to prevent rancidity?
A) Oxygen
B) Nitrogen
C) Carbon dioxide
D) Hydrogen
Answer: Nitrogen
49. Which of the following is a fast chemical reaction?
A) Rusting
B) Digestion
C) Burning of LPG
D) Fermentation
Answer: Burning of LPG
50. Which reaction involves absorption of energy?
A) Respiration
B) Combustion
C) Photosynthesis
D) Rusting
Answer: Photosynthesis