`NaNO_(3)` on heating with sodium hydroxide solution and zinc
liberates a gas which is also obtained by `:`

Options

A. heating `NH_(4)NO_(3)`
B. heating `NH_(4)NO_(2)` with sodium hydroxide solution.
C. heating `(NH_(4))_(2)Cr_(2)O_(7)`
D. heating `Ca(NO_(3))_(2)`.

Explanation

To solve the question, we need to analyze the reaction of sodium nitrate (NaNO₃) when heated with sodium hydroxide (NaOH) and zinc (Zn), and identify the gas liberated, which is also obtained from another reaction.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction in question is:
\[ \text{NaNO}_3 + \text{NaOH} + \text{Zn} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{NH}_3 + \text{H}_2\text{O} \]
From this reaction, we can see that ammonia (NH₃) is the gas liberated.

2. **Determine the Source of Ammonia**:
We need to find out which of the given reactions also produces ammonia gas (NH₃).

3. **Examine Each Option**:
- **Option 1**: Heating NH₄NO₃ (Ammonium Nitrate)
\[ \text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O} \]
This reaction produces nitrous oxide (N₂O) and does not yield ammonia. **Incorrect**.

- **Option 2**: Heating NH₄NO₂ (Ammonium Nitrite) with NaOH
\[ \text{NH}_4\text{NO}_2 + \text{NaOH} \rightarrow \text{NaNO}_2 + \text{NH}_3 + \text{H}_2\text{O} \]
This reaction produces ammonia gas. **Correct**.

- **Option 3**: Heating NH₄₂Cr₂O₇ (Ammonium Dichromate)
\[ \text{NH}_4\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + \text{Cr}_2\text{O}_3 + 4\text{H}_2\text{O} \]
This reaction produces nitrogen gas (N₂) and does not yield ammonia. **Incorrect**.

- **Option 4**: Heating Ca(NO₃)₂ (Calcium Nitrate)
\[ \text{Ca(NO}_3\text{)}_2 \rightarrow \text{CaO} + 2\text{NO}_2 + \text{O}_2 \]
This reaction produces nitrogen dioxide (NO₂) and oxygen (O₂), not ammonia. **Incorrect**.

4. **Conclusion**:
The only reaction that produces ammonia gas is the second option: heating NH₄NO₂ with sodium hydroxide.

### Final Answer:
The gas liberated when NaNO₃ is heated with sodium hydroxide and zinc is ammonia (NH₃), which is also obtained by heating NH₄NO₂ with sodium hydroxide.