Photochemical smog always contains

Options

A. `SO_(2)`
B. `O_(3)`
C. HNO_(3)`
D. All of these

Answer

To solve the question "Photochemical smog always contains", we will analyze the components of photochemical smog and determine the correct answer.

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that is formed when sunlight reacts with pollutants in the atmosphere. It typically occurs in urban areas during sunny days, especially in the summer.
- The primary pollutants involved in the formation of photochemical smog include nitrogen oxides (NOx) and volatile organic compounds (VOCs).

2. **Identifying Key Components**:
- The formation of photochemical smog leads to the generation of secondary pollutants, one of the most significant being ozone (O3).
- Other components that can be present in photochemical smog include various oxidants and secondary pollutants, but the focus here is on the specific options given in the question.

3. **Analyzing the Options**:
- The options provided are:
- A) SO2 (Sulfur Dioxide)
- B) O3 (Ozone)
- C) HNO3 (Nitric Acid)
- D) All of these
- We need to determine which of these components is always present in photochemical smog.

4. **Evaluating Each Option**:
- **SO2**: While sulfur dioxide can contribute to air pollution, it is not a primary component of photochemical smog. It is more associated with acid rain.
- **O3**: Ozone is a key component of photochemical smog and is formed as a secondary pollutant when sunlight reacts with nitrogen oxides and VOCs.
- **HNO3**: Nitric acid can be formed from nitrogen oxides but is not a defining characteristic of photochemical smog.
- **All of these**: Since SO2 and HNO3 are not always present in photochemical smog, this option is incorrect.

5. **Conclusion**:
- The only component that is always present in photochemical smog is ozone (O3). Therefore, the correct answer is **B) O3**.

### Final Answer:
Photochemical smog always contains **O3 (Ozone)**.

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