Which oxide of nitrogen condenses to a bluish liquid at `-30^@C`, but on warming it changes into reddish brown gas ?

Options

A. `N_2O_3`
B. `N_2O_5`
C. `N_2O_4`
D. `NO`

Answer

To solve the question, we need to identify the oxide of nitrogen that condenses to a bluish liquid at -30°C and changes to a reddish-brown gas upon warming.

### Step-by-Step Solution:

1. **Understanding Nitrogen Oxides**:
- There are several oxides of nitrogen, including NO (nitric oxide), NO2 (nitrogen dioxide), N2O (nitrous oxide), N2O3 (dinitrogen trioxide), and N2O5 (dinitrogen pentoxide). We need to focus on their physical states and colors.

2. **Identifying the Temperature and Color Change**:
- The question specifies a condensation to a bluish liquid at -30°C. This indicates that the oxide must have a boiling point around or below this temperature.
- Upon warming, it changes to a reddish-brown gas, which is a characteristic of certain nitrogen oxides.

3. **Analyzing N2O3**:
- Dinitrogen trioxide (N2O3) is known to condense into a blue liquid at low temperatures (around -30°C).
- When warmed, N2O3 decomposes into NO and NO2, with NO2 being a reddish-brown gas.

4. **Conclusion**:
- Based on the properties of nitrogen oxides, the oxide that fits the description of condensing to a bluish liquid at -30°C and changing to a reddish-brown gas upon warming is **N2O3 (dinitrogen trioxide)**.

### Final Answer:
The oxide of nitrogen that condenses to a bluish liquid at -30°C and changes to a reddish-brown gas upon warming is **N2O3 (dinitrogen trioxide)**.