To determine the correct set of species responsible for photochemical smog, we need to understand what photochemical smog is and which components contribute to its formation.
### 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). This reaction leads to the formation of secondary pollutants, including ozone (O3).
2. **Identifying Key Components**:
- The main components involved in the formation of photochemical smog include:
- Nitric Oxide (NO)
- Nitrogen Dioxide (NO2)
- Ozone (O3)
- Hydrocarbons (which are a source of VOCs)
3. **Analyzing the Options**:
- We have the following options:
- **Option A**: NO, NO2, O3, and hydrocarbons
- **Option B**: CO2, NO2, SO2, and hydrocarbons
- **Option C**: N2, NO2, and hydrocarbons
- **Option D**: N2, O2, O3, and hydrocarbons
4. **Evaluating Each Option**:
- **Option A**: Contains NO, NO2, O3, and hydrocarbons. This includes all the key components responsible for photochemical smog.
- **Option B**: CO2 and SO2 are not primary contributors to photochemical smog; they are more associated with other types of pollution.
- **Option C**: N2 is inert and does not contribute to photochemical reactions.
- **Option D**: N2 is inert, and while O3 is a component of smog, the presence of N2 and O2 does not contribute to the formation of photochemical smog.
5. **Conclusion**:
- The correct answer is **Option A**: NO, NO2, O3, and hydrocarbons, as these species are directly involved in the formation of photochemical smog.
