Which of the following is a secondary pollutant ?

Options

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

Answer

To determine which of the following is a secondary pollutant, let's follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Pollutants**:
- Pollutants are substances that cause pollution. They can be classified into two categories: primary pollutants and secondary pollutants.

2. **Identify Primary Pollutants**:
- Primary pollutants are those that are emitted directly from a source. Examples include carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2). These pollutants enter the atmosphere directly from sources like vehicles, industries, and natural events.

3. **Identify Secondary Pollutants**:
- Secondary pollutants are not emitted directly. Instead, they form in the atmosphere through chemical reactions involving primary pollutants. A well-known example of a secondary pollutant is ozone (O3), which forms when sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs).

4. **Analyze the Options**:
- Given the options:
- Carbon monoxide (CO) - Primary pollutant
- Sulfur dioxide (SO2) - Primary pollutant
- Nitrogen dioxide (NO2) - Primary pollutant
- Ozone (O3) - Secondary pollutant

5. **Conclusion**:
- Among the options provided, ozone (O3) is the only secondary pollutant. Therefore, the answer is ozone.

### Final Answer:
- The secondary pollutant among the options is **Ozone (O3)**.

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