Which of the following produces a coloured gas on heating?

Options

A. `NaNO_(3)`
B. `LiNO_(3)`
C. `MgCO_(3)`
D. `Li_(3)N`

Explanation

To determine which of the following compounds produces a colored gas upon heating, we will analyze each option systematically.

### Step-by-Step Solution:

1. **Analyze Option A: Sodium Nitrate (NaNO3)**
- When sodium nitrate is heated, it decomposes to form sodium nitrite (NaNO2) and oxygen gas (O2).
- The reaction can be represented as:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- Oxygen gas (O2) is colorless.
- **Conclusion**: This option does not produce a colored gas.

2. **Analyze Option B: Lithium Nitrate (LiNO3)**
- When lithium nitrate is heated, it decomposes to form lithium oxide (Li2O) and nitrogen dioxide (NO2).
- The reaction can be represented as:
\[ 2 \text{LiNO}_3 \rightarrow \text{Li}_2\text{O} + 2 \text{NO}_2 \]
- Nitrogen dioxide (NO2) is a reddish-brown gas.
- **Conclusion**: This option produces a colored gas.

3. **Analyze Option C: Magnesium Carbonate (MgCO3)**
- When magnesium carbonate is heated, it decomposes to form magnesium oxide (MgO) and carbon dioxide (CO2).
- The reaction can be represented as:
\[ \text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2 \]
- Carbon dioxide (CO2) is colorless.
- **Conclusion**: This option does not produce a colored gas.

4. **Analyze Option D: Lithium Nitride (Li3N)**
- When lithium nitride is heated, it decomposes to form lithium (Li) and nitrogen gas (N2).
- The reaction can be represented as:
\[ 2 \text{Li}_3\text{N} \rightarrow 6 \text{Li} + \text{N}_2 \]
- Nitrogen gas (N2) is colorless.
- **Conclusion**: This option does not produce a colored gas.

### Final Conclusion:
After analyzing all the options, the only compound that produces a colored gas upon heating is **Option B: Lithium Nitrate (LiNO3)**, which produces nitrogen dioxide (NO2), a reddish-brown gas.