Which of the following oxides of nitrogen is a brown coloured gas?

Options

A. `NO_(2)`
B. `NO`
C. `N_(2)O`
D. `N_(2)O_(4)`

Answer

To determine which oxide of nitrogen is a brown-colored gas, we can analyze the given options one by one.

### Step-by-Step Solution:

1. **Identify the Oxides of Nitrogen**:
The options provided are:
- NO2 (Nitrogen Dioxide)
- NO (Nitric Oxide)
- N2O (Nitrous Oxide)
- N2O4 (Dinitrogen Tetroxide)

2. **Analyze Each Option**:
- **NO2 (Nitrogen Dioxide)**:
- This gas is known to be brown in color. It is a significant pollutant and has a characteristic reddish-brown color.
- **NO (Nitric Oxide)**:
- This gas is colorless. It is a free radical and does not have any color.
- **N2O (Nitrous Oxide)**:
- Commonly known as laughing gas, it is also colorless and has non-flammable properties.
- **N2O4 (Dinitrogen Tetroxide)**:
- This gas is colorless at room temperature but can appear as a pale yellow or brownish color at higher concentrations. However, it is primarily considered colorless.

3. **Conclusion**:
Based on the analysis, the only oxide of nitrogen that is a brown-colored gas is **NO2 (Nitrogen Dioxide)**.

### Final Answer:
The brown-colored gas among the nitrogen oxides is **NO2 (Nitrogen Dioxide)**.

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