A photochemical reaction is

Options

A. catalysed by light
B. Initiated by light
C. accompanied with emission of light
D. accompanied with absorption of light

Explanation

**Step-by-Step Solution:**

1. **Understanding Photochemical Reactions:**
- A photochemical reaction is defined as a chemical reaction that occurs in the presence of light. The term "photo" refers to light, and "chemical" refers to the chemical changes that take place during the reaction.

2. **Key Characteristics:**
- These reactions require light to proceed; without light, the reaction cannot occur. This distinguishes photochemical reactions from other types of chemical reactions that may not need light.

3. **Example of a Photochemical Reaction:**
- A common example of a photochemical reaction is photosynthesis in plants. During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen using sunlight. This process is initiated by light, making it a photochemical reaction.

4. **Options Analysis:**
- The question provides several options:
- a) Catalyzed by light
- b) Initiated by light
- c) Accompanied with emission of light
- d) Accompanied with absorption of light
- Among these, the most accurate description of a photochemical reaction is that it is "initiated by light."

5. **Conclusion:**
- Therefore, the correct answer to the question "A photochemical reaction is" is option b) initiated by light.

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