Correct Option
The correct option is Photolytic decomposition.
Explanation
A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. Depending on the source of energy used to break the chemical bonds, decomposition reactions are classified into thermal (heat), electrolytic (electricity), and photolytic (light) decomposition.
Detailed Analysis
- Photolytic Decomposition: This type of reaction is driven by light energy. When silver chloride ($\text{AgCl}$), which is white in colour, is exposed to sunlight, it absorbs energy and decomposes into silver metal ($\text{Ag}$) and chlorine gas ($\text{Cl}_2$). The silver metal appears grey.
Reaction: $2\text{AgCl}(s) \xrightarrow{\text{Sunlight}} 2\text{Ag}(s) + \text{Cl}_2(g)$ - Thermal Decomposition: This requires heating (e.g., decomposition of calcium carbonate). It is not applicable here as sunlight provides light energy, not direct thermal heating in a furnace sense.
- Electrolytic Decomposition: This requires the passage of an electric current (e.g., electrolysis of water).
- Biological Decomposition: This refers to the breakdown of organic matter by microorganisms, which is unrelated to inorganic chemical salts like silver chloride.
Key Takeaway: The decomposition of silver salts (like silver chloride and silver bromide) in the presence of sunlight is a classic example of photolytic decomposition. This property is utilized in black and white photography.