Which of the following gases is not responsible for photochemical smog ?

Options

A. Oxides of nitrogen
B. Hydrocarbons
C. inert gases
D. Carbon monoxide

Explanation

To determine which gas is not responsible for photochemical smog, we need to understand what photochemical smog is and the gases involved in its formation.

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that is formed when sunlight reacts with pollutants such as volatile organic compounds (VOCs) and nitrogen oxides (NOx).

2. **Identifying Key Components**:
- The primary components of photochemical smog include:
- Ozone (O3)
- Nitrogen Dioxide (NO2)
- Peroxyacetyl Nitrate (PAN)
- Various hydrocarbons (especially unsaturated hydrocarbons)

3. **Analyzing the Gases**:
- Let's consider the gases typically involved in photochemical smog:
- **Nitrogen Oxides (NOx)**: These are responsible for the formation of ozone and PAN.
- **Hydrocarbons**: These are also precursors to the formation of ozone and contribute to smog.
- **Carbon Monoxide (CO)**: This is produced from incomplete combustion but does not directly contribute to the formation of photochemical smog.
- **Inert Gases**: Gases like helium or neon do not react chemically and are not involved in the formation of smog.

4. **Conclusion**:
- Among the gases mentioned, the inert gases do not participate in the chemical reactions that lead to photochemical smog. Therefore, the gas that is not responsible for photochemical smog is an inert gas.

### Final Answer:
The gas that is not responsible for photochemical smog is an **inert gas**.

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