Which of the following is a reddish-brown pollutant gas?

Options

A. HCL
B. Cl2
C. CO2
D. NO2

Answer

To solve the question "Which of the following is a reddish-brown pollutant gas?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a specific type of pollutant gas that is characterized by its reddish-brown color.

2. **Identify the Options**: The options provided are:
- HCl (Hydrochloric acid)
- Chlorine
- Carbon Dioxide
- Nitrogen Dioxide

3. **Analyze Each Option**:
- **HCl (Hydrochloric acid)**: This is a colorless gas and does not fit the description of reddish-brown.
- **Chlorine**: Chlorine is a greenish-yellow gas and also does not match the reddish-brown characteristic.
- **Carbon Dioxide**: This is a colorless gas and is not reddish-brown.
- **Nitrogen Dioxide**: This gas is known to be reddish-brown in color.

4. **Confirm the Characteristics of Nitrogen Dioxide**: Nitrogen dioxide (NO2) is a highly reactive gas that is produced from combustion processes, such as burning fossil fuels. It is known for its reddish-brown color and is a significant air pollutant.

5. **Conclusion**: Based on the analysis, the reddish-brown pollutant gas among the options provided is **Nitrogen Dioxide (NO2)**.

### Final Answer:
The reddish-brown pollutant gas is **Nitrogen Dioxide (NO2)**.

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