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

Options

A. `N_2 O`
B. `NO`
C. `N H_3`
D. `NO_2`

Explanation

To determine which of the following oxides of nitrogen is a colored gas, we will analyze each option provided:

1. **N2O (Nitrous Oxide)**:
- Nitrous oxide is commonly known as laughing gas. It is known to be a colorless gas. Therefore, it does not fit the criteria of being a colored gas.

2. **NO (Nitric Oxide)**:
- Nitric oxide is also a colorless gas. It does not exhibit any color, so it is not the colored gas we are looking for.

3. **NH3 (Ammonia)**:
- Ammonia is another colorless gas. It is widely used in various applications but does not have any color.

4. **NO2 (Nitrogen Dioxide)**:
- Nitrogen dioxide is a reddish-brown gas. The color is due to the presence of unpaired electrons in its molecular structure, which gives it paramagnetic properties. This makes NO2 the only colored gas among the options provided.

Based on the analysis, the oxide of nitrogen that is a colored gas is **NO2 (Nitrogen Dioxide)**.

**Final Answer**: NO2

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