In which salt,on heating gives a mixture of two gases is

Options

A. `NaNO_3`
B. `KNO_3`
C. `Pb(NO_3)_2`
D. `NH_4NO_3`

Explanation

To solve the question regarding which salt, upon heating, gives a mixture of two gases, we will analyze the thermal decomposition of the given salts: sodium nitrate, potassium nitrate, lead nitrate, and ammonium nitrate.

### Step-by-Step Solution:

1. **Identify the Salts**: The salts provided are:
- Sodium nitrate (NaNO3)
- Potassium nitrate (KNO3)
- Lead nitrate (Pb(NO3)2)
- Ammonium nitrate (NH4NO3)

2. **Thermal Decomposition of Sodium Nitrate**:
- When sodium nitrate is heated, it decomposes to form sodium nitrite (NaNO2) and oxygen gas (O2).
- Reaction:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- **Gases Produced**: Only oxygen (O2) is released.

3. **Thermal Decomposition of Potassium Nitrate**:
- When potassium nitrate is heated, it also decomposes similarly to sodium nitrate, producing potassium nitrite (KNO2) and oxygen gas (O2).
- Reaction:
\[ 2 \text{KNO}_3 \rightarrow 2 \text{KNO}_2 + \text{O}_2 \]
- **Gases Produced**: Only oxygen (O2) is released.

4. **Thermal Decomposition of Lead Nitrate**:
- When lead nitrate is heated, it decomposes to form lead(II) oxide (PbO), nitrogen dioxide (NO2), and oxygen gas (O2).
- Reaction:
\[ 2 \text{Pb(NO}_3)_2 \rightarrow 2 \text{PbO} + 4 \text{NO}_2 + \text{O}_2 \]
- **Gases Produced**: Nitrogen dioxide (NO2) and oxygen (O2) are released, which is a mixture of two gases.

5. **Thermal Decomposition of Ammonium Nitrate**:
- When ammonium nitrate is heated, it decomposes to form nitrous oxide (N2O) and water (H2O).
- Reaction:
\[ 2 \text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2 \text{H}_2\text{O} \]
- **Gases Produced**: Only nitrous oxide (N2O) is released.

6. **Conclusion**:
- Among the salts analyzed, only lead nitrate (Pb(NO3)2) produces a mixture of two gases (NO2 and O2) upon heating. Therefore, the correct answer is lead nitrate.

### Final Answer:
The salt that gives a mixture of two gases upon heating is **lead nitrate (Pb(NO3)2)**.