Which oxide of nitrogen is coloured gas?

Options

A. `N_2O`
B. `NO`
C. `N_2O_4`
D. `NO_2`

Answer

To determine which oxide of nitrogen is a colored gas, we can analyze the different nitrogen oxides provided in the question.

### Step-by-Step Solution:

1. **Identify the Oxides of Nitrogen**:
- The question mentions several nitrogen oxides: N2O (nitrous oxide), NO (nitric oxide), N2O4 (dinitrogen tetroxide), and NO2 (nitrogen dioxide).

2. **Analyze Each Oxide**:
- **N2O (Nitrous Oxide)**:
- This is a colorless gas, commonly known as laughing gas. It is non-flammable and has a metallic scent.
- **NO (Nitric Oxide)**:
- This is also a colorless gas and acts as a free radical due to the presence of unpaired electrons.
- **N2O4 (Dinitrogen Tetroxide)**:
- This gas is colorless and exists in equilibrium with nitrogen dioxide (NO2). It is used as a powerful oxidizer.
- **NO2 (Nitrogen Dioxide)**:
- This gas is paramagnetic, meaning it has unpaired electrons. At higher temperatures, it appears as a reddish-brown gas.

3. **Determine the Colored Gas**:
- Among the oxides analyzed, NO2 is the only one that is colored. It is reddish-brown due to its paramagnetic nature, which arises from the presence of unpaired electrons.

4. **Conclusion**:
- Therefore, the oxide of nitrogen that is a colored gas is **NO2 (Nitrogen Dioxide)**.

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

---