Q1. [1] § 1.2 TYPES OF CHEMICAL REACTIONS § 1.2.1 Combination Reaction § 1.2.2 Decomposition Reaction
Select from the following a decomposition reaction in which source of energy for decomposition is light :
- (a) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
- (b) 2H₂O → 2H₂ + O₂
- (c) 2AgBr → 2Ag + Br₂
- (d) CaCO₃ → CaO + CO₂
Previously asked in CBSE board exam
2024 31/1/1 Q2
Generated by claude-sonnet-4-6 · 2026-06-14 10:28 · grounding rag
Model Answer
(c) 2AgBr → 2Ag + Br₂
This is a photochemical decomposition reaction where silver bromide decomposes in the presence of sunlight (light energy) to form silver and bromine.
Explanation
- Option (a) uses heat; option (b) uses electricity; option (d) uses heat — all are thermal decomposition reactions.
- 2AgBr → 2Ag + Br₂ is a classic photochemical decomposition (light as energy source), used as the standard textbook example.
- Examiners expect students to distinguish between heat, light, and electricity as energy sources in decomposition reactions (as asked in Exercise Q.12 of Chapter 1).
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