AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Silver chloride (AgCl) undergoes photodecomposition when exposed to sunlight (light energy). The reaction is:
$$2\text{AgCl}(s) \xrightarrow{\text{sunlight}} 2\text{Ag}(s) + \text{Cl}_2(g)$$
AgCl decomposes into silver metal and chlorine gas, turning grey. Dark-coloured bottles prevent light from reaching the compound, thus stopping this decomposition.
This is a photochemical decomposition reaction — a type of decomposition triggered by light, not heat. Examiners expect: (1) naming the type of reaction, (2) the balanced equation, and (3) the practical reason for dark bottles. The textbook uses AgCl as a standard example of photodecomposition, so memorise the equation. Note: the source passages mention corrosion of silver (with sulphur), but the photodecomposition of AgCl is the standard NCERT Class 10 Chemistry example from Chapter 1 (decomposition reactions section).