Photochemical smog consists of excessive amount of X, in addition to aldehydes, ketones, peroxyacetyl nitrate (PAN), and so forthe X is:

Options

A. CO
B. `CH_(4)`
C. `O_(3)`
D. `CO_(2)`

Explanation

To solve the question regarding the components of photochemical smog, we need to identify the substance represented by "X" in the context of the pollutants mentioned (aldehydes, ketones, peroxyacetyl nitrate).

### 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 nitrogen oxides and volatile organic compounds (VOCs).

2. **Identifying the Components**:
- The question states that photochemical smog contains excessive amounts of "X," along with aldehydes, ketones, and peroxyacetyl nitrate (PAN).

3. **Recognizing the Role of Ozone**:
- One of the primary components of photochemical smog is ozone (O₃). It is formed when ultraviolet (UV) light from the sun reacts with nitrogen oxides and VOCs in the atmosphere.

4. **Summarizing the Reactions**:
- The reactions involved in the formation of photochemical smog include:
- Nitrogen oxides (NO and NO₂) reacting with UV light to produce ozone.
- Ozone then reacts with hydrocarbons to form aldehydes and ketones.

5. **Conclusion**:
- Given that ozone is a significant component of photochemical smog and is not listed among the other pollutants (aldehydes, ketones, PAN), we can conclude that "X" is ozone.

### Final Answer:
The substance "X" in photochemical smog is **ozone (O₃)**.