The gas/es involved in the formation of photochemical fog are

Options

A. `CO_(2)`
B. `SO_(2)`
C. NO
D. none of these

Answer

To answer the question regarding the gases involved in the formation of photochemical fog, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photochemical Fog**:
- Photochemical fog, also known as photochemical smog, is a type of air pollution that occurs when sunlight reacts with pollutants in the atmosphere.

2. **Identifying Key Pollutants**:
- The primary pollutants involved in the formation of photochemical fog include unsaturated hydrocarbons (like those released from vehicles) and nitrogen oxides (NOx), particularly nitric oxide (NO) and nitrogen dioxide (NO2).

3. **Source of Pollutants**:
- These pollutants are primarily emitted from automobiles and industrial processes, particularly during the combustion of fossil fuels such as petrol and diesel.

4. **Chemical Reactions**:
- When sunlight interacts with these pollutants, a series of chemical reactions occur:
- Nitric oxide (NO) is oxidized to nitrogen dioxide (NO2).
- NO2 absorbs sunlight and breaks down into NO and free oxygen atoms (O).
- The free oxygen atoms react with molecular oxygen (O2) to form ozone (O3).

5. **Formation of Photochemical Smog**:
- Ozone (O3) and nitrogen dioxide (NO2) are significant components of photochemical smog. Ozone is a strong oxidizing agent and reacts with hydrocarbons to form various organic compounds, contributing to the smog's formation.

6. **Conclusion**:
- Among the options provided (CO2, SO2, NO, none of these), the gas that is directly involved in the formation of photochemical fog is **NO (nitric oxide)**.

### Final Answer:
The gas involved in the formation of photochemical fog is **NO (nitric oxide)**.

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