Which of the following is not a pollutant ?

Options

A. `CO_2`
B. `NO_2`
C. `H_2O`
D. `SO_2`

Answer

To determine which of the following is not a pollutant, we need to analyze each option provided.

### Step-by-Step Solution:

1. **Understand the Definition of a Pollutant**: A pollutant is defined as a substance that causes pollution, which can be harmful to the environment and living organisms.

2. **Evaluate the Options**: We need to assess each of the given substances to see if they qualify as pollutants.

3. **Analyze CO2 (Carbon Dioxide)**:
- CO2 is produced from burning fossil fuels, biomass, and other carbon-containing materials.
- It contributes to greenhouse gas emissions and climate change.
- **Conclusion**: CO2 is a pollutant.

4. **Analyze NO2 (Nitrogen Dioxide)**:
- NO2 is produced from combustion processes, such as vehicle engines and power plants.
- It is a toxic gas that can cause respiratory problems and contributes to the formation of smog.
- **Conclusion**: NO2 is a pollutant.

5. **Analyze SO2 (Sulfur Dioxide)**:
- SO2 is released from burning fossil fuels that contain sulfur, such as coal and oil.
- It can lead to acid rain and respiratory issues.
- **Conclusion**: SO2 is a pollutant.

6. **Analyze H2O (Water)**:
- H2O is essential for life and is not harmful in its pure form.
- While water can become a pollutant when contaminated, pure water itself is not a pollutant.
- **Conclusion**: H2O is not a pollutant.

7. **Final Answer**: Among the options provided, the substance that is not a pollutant is **H2O (water)**.