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 given compounds produces a colored gas upon heating, we will analyze each option step by step.

### Step 1: Analyze NaNO3 (Sodium Nitrate)
- **Reaction**: When sodium nitrate (NaNO3) is heated, it decomposes to produce sodium nitrite (NaNO2) and oxygen (O2).
- **Products**:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- **Gas Produced**: The oxygen gas produced is colorless.

**Hint**: Check if the gas produced is colored or colorless.

### Step 2: Analyze LiNO3 (Lithium Nitrate)
- **Reaction**: When lithium nitrate (LiNO3) is heated, it decomposes to produce lithium oxide (Li2O), nitrogen dioxide (NO2), and oxygen (O2).
- **Products**:
\[ 2 \text{LiNO}_3 \rightarrow \text{Li}_2\text{O} + 2 \text{NO}_2 + \text{O}_2 \]
- **Gas Produced**: Nitrogen dioxide (NO2) is a reddish-brown gas.

**Hint**: Look for any colored gases in the products of the reaction.

### Step 3: Analyze MgCO3 (Magnesium Carbonate)
- **Reaction**: When magnesium carbonate (MgCO3) is heated, it decomposes to produce magnesium oxide (MgO) and carbon dioxide (CO2).
- **Products**:
\[ \text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2 \]
- **Gas Produced**: Carbon dioxide (CO2) is colorless.

**Hint**: Determine if the gas produced is colored or not.

### Step 4: Analyze Li3N (Lithium Nitride)
- **Reaction**: When lithium nitride (Li3N) is heated, it decomposes to produce lithium (Li) and nitrogen gas (N2).
- **Products**:
\[ 2 \text{Li}_3\text{N} \rightarrow 6 \text{Li} + \text{N}_2 \]
- **Gas Produced**: Nitrogen gas (N2) is colorless.

**Hint**: Assess whether the gas produced has any color.

### Conclusion
After analyzing all the options:
- **NaNO3** produces colorless oxygen.
- **LiNO3** produces reddish-brown nitrogen dioxide (NO2), which is colored.
- **MgCO3** produces colorless carbon dioxide.
- **Li3N** produces colorless nitrogen.

Thus, the only compound that produces a colored gas upon heating is **LiNO3** (Lithium Nitrate), which produces reddish-brown nitrogen dioxide (NO2).

**Final Answer**: **LiNO3 produces a colored gas (reddish-brown NO2) upon heating.**