`(NH_(4))_(2)Cr_(2)O_(7)` on heating liberates a gas. The same gas will be obtained by

Options

A. Heating `NH_(4)NO_(2)`
B. Heating `NH_(4)NO_(3)`
C. Heating `(NH_(4))_(2)SO_(4)`
D. Treatment `Mg_(3)N_(2)` with `H_(2)O`

Explanation

To solve the problem, we need to determine the gas liberated when `(NH4)2Cr2O7` (ammonium dichromate) is heated and identify another reaction that produces the same gas.

### Step-by-Step Solution:

1. **Identify the Compound**: The compound given is ammonium dichromate, `(NH4)2Cr2O7`.

2. **Heating the Compound**: When ammonium dichromate is heated, it undergoes thermal decomposition. The reaction can be represented as:
\[ (NH4)2Cr2O7 \xrightarrow{\text{heat}} Cr2O3 + N2 + 4H2O \]
From this reaction, we can see that nitrogen gas (N2) is one of the products.

3. **Identify the Gas**: The gas liberated during the heating of ammonium dichromate is nitrogen gas (N2).

4. **Finding Another Reaction**: We need to find another reaction that produces nitrogen gas (N2). One common reaction that produces nitrogen gas is the decomposition of ammonium nitrite:
\[ NH4NO2 \xrightarrow{\text{heat}} N2 + 2H2O \]
This reaction also produces nitrogen gas (N2).

5. **Conclusion**: Therefore, the same gas (N2) can be obtained by heating ammonium nitrite `(NH4NO2)`.

### Final Answer:
The gas liberated when `(NH4)2Cr2O7` is heated is nitrogen gas (N2), and it can also be obtained by heating ammonium nitrite `(NH4NO2)`.