Which of the following cause photochemical smog?

Options

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

Answer

**Step-by-Step Text Solution:**

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that occurs when sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere.
- It is characterized by a brownish haze and is most prevalent in urban areas during sunny, warm conditions, particularly in the morning and afternoon.

2. **Identifying the Components**:
- The primary components that lead to the formation of photochemical smog are nitrogen oxides (NO2) and volatile organic compounds (VOCs).
- Nitrogen oxides are mainly produced from sources such as vehicle emissions, coal power plants, and industrial activities.

3. **Analyzing the Options**:
- The question provides several options to identify which one contributes to photochemical smog.
- Let's evaluate each option:
- **O2 (Oxygen)**: This is essential for life but does not contribute to photochemical smog. (Incorrect)
- **CO2 (Carbon Dioxide)**: While it is a greenhouse gas and is inhaled by plants, it does not play a role in the formation of photochemical smog. (Incorrect)
- **CH4 (Methane)**: Although it is a volatile organic compound, it is not a direct contributor to the formation of photochemical smog. (Incorrect)
- **NO2 (Nitrogen Dioxide)**: This is a nitrogen oxide that directly contributes to the formation of photochemical smog when it reacts with sunlight. (Correct)

4. **Conclusion**:
- The correct answer is **NO2 (Nitrogen Dioxide)**, as it is a key component in the formation of photochemical smog.