Pure`N_2` gas is obtained from

Options

A. `NH_3 + NaNO_2`
B. `NH_4 Cl + NaNO_2`
C. `N_2 O + Cu`
D. `(NH_4)_2 Cr_2 O_7`

Explanation

To obtain pure nitrogen gas (N₂), we can follow a specific chemical reaction sequence. Here’s a step-by-step breakdown of how to achieve this:

### Step-by-Step Solution:

1. **Identify the Reactants**: The first step is to recognize the reactants involved in the reaction. In this case, we will use ammonium fluoride (NH₄F) and sodium nitrite (NaNO₂).

2. **Reaction of Ammonium Fluoride with Sodium Nitrite**: When ammonium fluoride reacts with sodium nitrite, it produces ammonium nitrite (NH₄NO₂) and sodium chloride (NaCl). The reaction can be represented as:
\[ NH₄F + NaNO₂ \rightarrow NH₄NO₂ + NaCl \]

3. **Decomposition of Ammonium Nitrite**: The next step involves heating the ammonium nitrite (NH₄NO₂). Upon heating, ammonium nitrite decomposes to produce nitrogen gas (N₂) and water (H₂O):
\[ 2 NH₄NO₂ \rightarrow N₂ + 2 H₂O \]

4. **Collection of Pure Nitrogen Gas**: The nitrogen gas produced from the decomposition can be collected as it is released during the reaction. The water formed will be in liquid form and can be removed or allowed to condense separately.

5. **Final Product**: The final product of this reaction sequence is pure nitrogen gas (N₂).

### Summary of Reaction Sequence:
- Ammonium fluoride reacts with sodium nitrite to form ammonium nitrite and sodium chloride.
- Ammonium nitrite is then heated to produce nitrogen gas and water.