Photochemical smog is formed by :

Options

A. `NO`
B. `NO_(2)`
C. `CH_(3)-underset(O)underset(||)COO-NO_(2)`
D. `CH_(2)=CH-CH=O`

Answer

To solve the question regarding the formation of photochemical smog, we can break it down into a few steps:

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that occurs when sunlight reacts with pollutants in the atmosphere.

2. **Identifying Key Components**:
- The primary components involved in the formation of photochemical smog include nitrogen oxides (NOx), volatile organic compounds (VOCs), and ozone (O3).

3. **Role of UV Radiation**:
- Ultraviolet (UV) radiation from the sun plays a crucial role in the chemical reactions that lead to the formation of photochemical smog.

4. **Chemical Reactions**:
- When UV light interacts with nitrogen oxides (NOx), it leads to the formation of ozone (O3) and other secondary pollutants.
- The reaction can be summarized as follows:
- NO2 (nitrogen dioxide) can be photolyzed by UV light to produce NO (nitric oxide) and O (atomic oxygen).
- The atomic oxygen can then react with molecular oxygen (O2) to form ozone (O3).

5. **Formation of PAN**:
- In addition to ozone, photochemical smog also contains peroxyacetyl nitrate (PAN), which is formed from the reaction of VOCs with nitrogen oxides in the presence of sunlight.

6. **Conclusion**:
- Therefore, photochemical smog is primarily formed by the reaction of UV radiation with nitrogen oxides and volatile organic compounds, resulting in the production of ozone and PAN.

### Final Answer:
Photochemical smog is formed by the reaction of UV radiation on nitrogen oxides (NOx) and volatile organic compounds (VOCs).