Nitrogen gas is prepared :

Options

A. by heating ammonium nitrate
B. by reacting excess chlorine with liquor ammonia
C. by passing `HNO_(3)` vapours on red hot copper.
D. by heating lead nitrate

Explanation

To solve the question regarding the preparation of nitrogen gas, we will analyze each option provided and determine which one correctly produces nitrogen gas (N2).

### Step-by-Step Solution:

1. **Option A: Heating Ammonium Nitrate (NH4NO3)**
- When ammonium nitrate is heated, it decomposes to form nitrous oxide (N2O) and water (H2O).
- The reaction can be represented as:
\[ 2 NH_4NO_3 \rightarrow N_2O + 2 H_2O \]
- Since nitrogen gas (N2) is not produced in this reaction, **Option A is incorrect**.

2. **Option B: Reacting Excess Chlorine with Ammonia (NH3)**
- The reaction of ammonia with excess chlorine produces nitrogen gas and ammonium chloride (NH4Cl).
- The balanced reaction is:
\[ 8 NH_3 + 3 Cl_2 \rightarrow N_2 + 6 NH_4Cl \]
- Here, nitrogen gas (N2) is produced, so **Option B is correct**.

3. **Option C: Passing HNO3 Vapors on Red Hot Copper**
- When concentrated nitric acid (HNO3) is passed over red hot copper, copper is oxidized, and nitrogen gas is produced.
- The balanced reaction is:
\[ 5 Cu + 2 HNO_3 \rightarrow 5 CuO + N_2 + 2 H_2O \]
- Since nitrogen gas (N2) is produced, **Option C is also correct**.

4. **Option D: Heating Lead Nitrate (Pb(NO3)2)**
- When lead nitrate is heated, it decomposes to form lead oxide (PbO), nitrogen dioxide (NO2), and oxygen (O2).
- The reaction can be represented as:
\[ 2 Pb(NO_3)_2 \rightarrow 2 PbO + 4 NO_2 + O_2 \]
- Since nitrogen gas (N2) is not produced in this reaction, **Option D is incorrect**.

### Conclusion:
The correct options for the preparation of nitrogen gas are **Option B** (reacting excess chlorine with ammonia) and **Option C** (passing HNO3 vapors on red hot copper).