White silver chloride turns grey in sunlight. What type of reaction is this?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Decomposition
In a decomposition reaction, a single compound breaks down into two or more simpler substances. In sunlight, silver chloride breaks down into silver, which is grey, and chlorine gas:
\(\ce{2AgCl}\xrightarrow{\text{sunlight}}\ce{2Ag + Cl2}\)
Because the energy for the change comes from light, this is called a photolytic decomposition. The same reaction is used in black-and-white photography.
Why the other options are incorrect
Option (1) Combination — Incorrect. Two or more substances join to form one product, the reverse of what happens here.
Option (3) Oxidation — Incorrect. It is the gain of oxygen or loss of hydrogen by a substance; silver chloride takes up no oxygen here, it breaks apart.
Option (4) Displacement — Incorrect. A more reactive element pushes a less reactive one out of its compound; here no second substance takes part.