Photochemical smog involves

Options

A. `O_(3)`
B. NO
C. `NO_(2)`
D. All of these

Answer

### 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 (NOx) and volatile organic compounds (VOCs) in the atmosphere.

2. **Components of Photochemical Smog**:
- The primary components involved in the formation of photochemical smog include:
- **Nitrogen Oxides (NOx)**: These are produced from the combustion of fossil fuels in vehicles and industrial processes.
- **Volatile Organic Compounds (VOCs)**: These are unburned hydrocarbons that also come from vehicle emissions and industrial activities.
- **Ozone (O3)**: While ozone is beneficial in the upper atmosphere, at ground level, it is a harmful pollutant formed during the photochemical reactions.

3. **Formation Process**:
- When fossil fuels are burned, they release nitrogen oxides and unburned hydrocarbons into the atmosphere.
- Under the influence of sunlight, nitrogen oxides can react to form nitrogen dioxide (NO2).
- The sunlight also facilitates reactions between nitrogen dioxide and unburned hydrocarbons, leading to the formation of ozone and other secondary pollutants like formaldehyde and peroxyacetylnitrate.

4. **Conclusion**:
- Therefore, photochemical smog involves a mixture of ozone, nitrogen oxides (both nitric oxide and nitrogen dioxide), and unburned hydrocarbons.
- The correct answer to the question is that photochemical smog involves all of these components.

### Final Answer:
Photochemical smog involves ozone, nitric oxide, nitrogen dioxide, and unburned hydrocarbons. Thus, the correct option is "all of these."

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