Which of the following is a secondary pollutant ? (A) O3 (B) SO2 (C) CO2 (D) CO

Options

A. `O_(3)`
B. `SO_(2)`
C. `CO_(2)`
D. `CO`

Answer

To determine which of the following is a secondary pollutant, we need to understand the difference between primary and secondary pollutants.

### Step-by-Step Solution:

1. **Define Primary Pollutants**:
- Primary pollutants are substances that are directly emitted into the atmosphere from a source. Examples include carbon monoxide (CO), sulfur dioxide (SO2), and carbon dioxide (CO2).

2. **Define Secondary Pollutants**:
- Secondary pollutants are not emitted directly. Instead, they form in the atmosphere through chemical reactions between primary pollutants or other substances.

3. **Analyze the Options**:
- **Option A: O3 (Ozone)**: Ozone is formed when primary pollutants like hydrocarbons and nitrogen oxides react in the presence of sunlight. Therefore, it is a secondary pollutant.
- **Option B: SO2 (Sulfur Dioxide)**: This is a primary pollutant as it is emitted directly from sources like burning fossil fuels.
- **Option C: CO2 (Carbon Dioxide)**: This is also a primary pollutant, released directly from combustion processes.
- **Option D: CO (Carbon Monoxide)**: This is another example of a primary pollutant, produced from incomplete combustion of carbon-containing fuels.

4. **Conclusion**:
- The only option that qualifies as a secondary pollutant is **Option A: O3 (Ozone)**.

### Final Answer:
The correct answer is **(A) O3**.

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