Which of these is not an air pollutant?

Options

A. Carbon monoxide
B. Sulphur dioxide
C. Lead
D. Oxygen

Explanation

To determine which of the given options is not an air pollutant, we can analyze each option based on the definition of an air pollutant.

### Step-by-Step Solution:

1. **Understand the Definition of Air Pollutants**:
- An air pollutant is a substance that is present in the air in excess amounts and has negative effects on health and the environment.

2. **Analyze Each Option**:
- **Carbon Monoxide (CO)**:
- This is a colorless, odorless gas that can interfere with the blood's ability to carry oxygen. It is produced from incomplete combustion of fossil fuels and is harmful to health. Therefore, it is an air pollutant.

- **Sulfur Dioxide (SO₂)**:
- This gas is produced from burning fossil fuels and can cause respiratory problems and contribute to acid rain. It is harmful in high concentrations, making it an air pollutant.

- **Lead (Pb)**:
- Lead is a heavy metal that can have severe health effects, including brain damage and kidney damage. It is released into the air through industrial processes and is considered an air pollutant.

- **Oxygen (O₂)**:
- Oxygen is essential for life and is required for respiration in humans and animals. It is not harmful and is not present in excess amounts; rather, it is necessary for metabolic processes. Therefore, oxygen is not an air pollutant.

3. **Conclusion**:
- Among the options provided, the substance that is not an air pollutant is **Oxygen**.

### Final Answer:
**Oxygen is not an air pollutant.**

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