Chapter 10 — Types of Chemical Reactions: Multiple Choice Questions
Instructions: Each question carries 1 mark. Choose the best answer.
1. In the reaction A + B → AB, the type of reaction is ______.
Answer
(a) Decomposition (b) Combination (c) Displacement (d) Double displacement
✅ Answer: (b) Combination
ExplanationCombination (Synthesis) reaction: Two or more reactants combine to form a single product. Example: 2Mg + O₂ → 2MgO (magnesium burns in oxygen). The reaction A + B → AB is the general form.
2. Decomposition of water by electricity is called ______.
Answer
(a) Thermolysis (b) Photolysis (c) Electrolysis (d) Hydrolysis
✅ Answer: (c) Electrolysis
ExplanationDecomposition can be caused by heat (thermolysis/thermal decomposition), light (photolysis), or electricity (electrolysis). Decomposition of water (2H₂O → 2H₂ + O₂) by passing electric current is electrolysis. Water (hydrolysis) refers to reactions with water.
3. The reaction between an acid and a base to form salt and water is called ______.
Answer
(a) Decomposition (b) Combination (c) Neutralisation (d) Displacement
✅ Answer: (c) Neutralisation
ExplanationNeutralisation: Acid + Base → Salt + Water Example: HCl + NaOH → NaCl + H₂O The acid and base neutralise each other. The reaction is exothermic and the solution becomes neutral (pH = 7) if stoichiometric amounts are used.
4. In the reaction: Zn + CuSO₄ → ZnSO₄ + Cu, the type is ______.
Answer
(a) Combination (b) Decomposition (c) Single displacement (d) Double displacement
✅ Answer: (c) Single displacement
ExplanationIn a single displacement (substitution) reaction, a more active/reactive element displaces a less reactive element from its compound. Here, Zinc (more reactive) displaces Copper from copper sulphate. General form: A + BC → AC + B.
5. The reaction: AgNO₃ + NaCl → AgCl↓ + NaNO₃ is an example of ______.
Answer
(a) Single displacement (b) Double displacement (c) Combination (d) Decomposition
✅ Answer: (b) Double displacement
ExplanationIn a double displacement (metathesis) reaction, the ions of two compounds exchange partners. The ↓ symbol indicates a precipitate forms (AgCl is insoluble). General form: AB + CD → AD + CB.
6. In a redox reaction, the substance that loses electrons is ______.
Answer
(a) Oxidising agent and is reduced (b) Reducing agent and is oxidised (c) Oxidising agent and is oxidised (d) Reducing agent and is reduced
✅ Answer: (b) Reducing agent and is oxidised
Explanation
- Oxidation = loss of electrons → the substance is oxidised → it acts as a reducing agent (it reduces the other substance by giving electrons)
- Reduction = gain of electrons → the substance is reduced → it acts as an oxidising agent
Memory trick: OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons)
7. Rusting of iron is an example of ______.
Answer
(a) Reduction (b) Oxidation (c) Decomposition (d) Displacement
✅ Answer: (b) Oxidation
ExplanationRusting: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → 2Fe₂O₃·3H₂O (rust) Iron gains oxygen (oxidation) and also loses electrons (Fe → Fe³⁺). Both definitions confirm it is oxidation. Rust = hydrated iron(III) oxide. Conditions: presence of water and oxygen.
8. Photosynthesis is an example of ______.
Answer
(a) Endothermic and combination reaction (b) Exothermic and decomposition reaction (c) Endothermic and redox reaction (d) Exothermic and combination reaction
✅ Answer: (c) Endothermic and redox reaction
ExplanationPhotosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (using sunlight)
- It is endothermic — absorbs light energy from the sun
- It is a redox reaction — CO₂ is reduced (gains H) and H₂O is oxidised (loses H, O is released)
- It is also a combination-type (CO₂ and H₂O combine to form glucose)
9. Burning of fuels (combustion) is an example of ______.
Answer
(a) Endothermic reaction (b) Exothermic reaction (c) Decomposition (d) Combination without oxidation
✅ Answer: (b) Exothermic reaction
ExplanationCombustion: CH₄ + 2O₂ → CO₂ + 2H₂O + heat and light Combustion is always exothermic — it releases energy. It is also a redox reaction (fuel is oxidised). Reactions that release heat are exothermic (negative ΔH). Reactions that absorb heat are endothermic (positive ΔH).
10. In the reaction CaCO₃ → CaO + CO₂, the type is ______.
Answer
(a) Combination (b) Displacement (c) Decomposition (d) Double displacement
✅ Answer: (c) Decomposition
ExplanationCalcium carbonate (limestone) decomposes on heating to give calcium oxide (quicklime) and carbon dioxide. One compound breaks into two simpler substances = decomposition. This is an endothermic thermal decomposition used in making cement.
Quick Revision — Types of Reactions
| Type | Pattern | Example |
|---|
| Combination | A + B → AB | 2H₂ + O₂ → 2H₂O |
| Decomposition | AB → A + B | 2H₂O → 2H₂ + O₂ |
| Single displacement | A + BC → AC + B | Fe + CuSO₄ → FeSO₄ + Cu |
| Double displacement | AB + CD → AD + CB | AgNO₃ + NaCl → AgCl + NaNO₃ |
| Neutralisation | Acid + Base → Salt + H₂O | HCl + NaOH → NaCl + H₂O |
| Combustion | Fuel + O₂ → CO₂ + H₂O + energy | CH₄ + 2O₂ → CO₂ + 2H₂O |
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