A: Photochemical smog is also known as oxidising smog.
R: Photochemical smog is chiefly composed of `O_(3)` PAN, etc.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4).

Answer

To analyze the statements regarding photochemical smog, we can break down the assertion and reason step by step.

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that occurs when sunlight reacts with pollutants such as volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the atmosphere.
- It is characterized by the presence of ozone (O₃) and other oxidizing agents.

**Hint**: Remember that photochemical smog forms primarily due to reactions involving sunlight and certain pollutants.

2. **Assertion Analysis**:
- The assertion states that "Photochemical smog is also known as oxidizing smog."
- This is true because photochemical smog contains a high concentration of oxidizing agents, particularly ozone, which is a strong oxidizer.

**Hint**: Think about the chemical nature of the components in photochemical smog and their effects on the environment.

3. **Reason Analysis**:
- The reason states that "Photochemical smog is chiefly composed of O₃ (ozone), PAN (peroxyacetyl nitrate), etc."
- This is also true. Photochemical smog primarily consists of ozone and PAN, which are formed from reactions involving nitrogen oxides and volatile organic compounds in the presence of sunlight.

**Hint**: Recall the chemical reactions that lead to the formation of ozone and PAN in the atmosphere.

4. **Conclusion**:
- Both the assertion and the reason are correct. The reason provided gives a correct explanation for the assertion. Therefore, we conclude that both statements are true and the reason is a correct explanation for the assertion.

**Hint**: When evaluating assertions and reasons, check if the reason logically supports the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.