Which one of the following reactions is an example of decomposition

Which one of the following reactions is an example of decomposition reaction?

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
2AgCl(s) Sunlight → 2Ag(s) + Cl₂(g)
CuO + H₂ Heat → Cu + H₂O
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
This question was previously asked in
UPSC NDA-1 – 2022
The correct option is B.
A decomposition reaction is a reaction in which a single compound breaks down into two or more simpler substances.
Option A is a combustion reaction, where a substance reacts rapidly with oxygen to produce heat and light.
Option B, $2\text{AgCl(s)} \text{ Sunlight} \rightarrow 2\text{Ag(s)} + \text{Cl}_2\text{(g)}$, shows silver chloride (a single compound) breaking down into silver and chlorine (simpler substances) upon exposure to sunlight. This is a classic example of photolytic decomposition.
Option C is a reduction reaction, specifically the reduction of copper(II) oxide by hydrogen.
Option D is a displacement reaction, where iron displaces copper from copper sulphate solution.