Which of the following is a secondary pollutant ?

Options

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

Answer

To determine which of the following is a secondary pollutant, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Primary Pollutants**: These are pollutants that are directly emitted from a source into the environment. Examples include substances like Sulphur Dioxide (SO2), Carbon Monoxide (CO), and Ammonia (NH3).
- **Secondary Pollutants**: These are not emitted directly. Instead, they are formed in the atmosphere through chemical reactions involving primary pollutants. This process often requires sunlight, known as photochemical reactions.

2. **Identify the Options**:
- We are provided with four options to identify which one is a secondary pollutant.

3. **Evaluate Each Option**:
- **Option 1: Sulphur Dioxide (SO2)**: This is a primary pollutant as it is emitted directly from sources like burning fossil fuels.
- **Option 2: Carbon Monoxide (CO)**: This is also a primary pollutant, produced from incomplete combustion of carbon-containing fuels.
- **Option 3: Ozone (O3)**: This is a secondary pollutant formed by the reaction of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.
- **Option 4: Nitrogen Dioxide (NO2)**: This is a primary pollutant, which is emitted from vehicle exhaust and industrial processes.

4. **Select the Correct Option**:
- After evaluating all options, we find that **Option 3: Ozone (O3)** is the only secondary pollutant among the choices provided.

### Final Answer:
The correct option is **Ozone (O3)**, which is a secondary pollutant.

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