An example of photochemical reaction is

Options

A. Darkening of silver chloride in light
B. Blackening of white lead upon prolonged exposure to air
C. Rusting of iron in moist air
D. Glowing of charcoal

Answer

To determine an example of a photochemical reaction, we need to understand what a photochemical reaction is. A photochemical reaction is a chemical reaction that occurs in the presence of light, typically sunlight.

### Step-by-Step Solution:

1. **Definition of Photochemical Reaction**: A photochemical reaction is defined as a chemical reaction that is initiated or accelerated by the absorption of light.

2. **Identifying Examples**: We need to evaluate the options provided to identify which one represents a photochemical reaction.

3. **Option Analysis**:
- **Option 1**: The darkening of silver chloride in light.
- When silver chloride (AgCl) is exposed to sunlight, it decomposes to form silver (Ag) and chlorine gas (Cl2), resulting in a darkening effect. This is indeed a photochemical reaction as it occurs in the presence of light.

- **Option 2**: Blackening of white lead upon prolonged exposure to air.
- This is not a photochemical reaction as it does not involve light directly causing a chemical change.

- **Option 3**: Rusting of iron.
- Rusting is an electrochemical process and does not involve light as a primary factor, so it is not a photochemical reaction.

- **Option 4**: Glowing of charcoal.
- This is a physical change due to combustion and does not involve a chemical reaction initiated by light.

4. **Conclusion**: Based on the analysis, the correct answer is the first option: the darkening of silver chloride in light, as it is a clear example of a photochemical reaction.

### Final Answer:
An example of a photochemical reaction is the darkening of silver chloride in light.

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