All ammonium salts liberate ammonia when :

Options

A. heated alone
B. heated with caustic soda
C. heated with `H_(2)SO_(4)`
D. heated with `NaNO_(2)`

Explanation

To solve the question "All ammonium salts liberate ammonia when:", we need to analyze the options provided and understand the conditions under which ammonium salts release ammonia (NH3).

### Step-by-Step Solution:

1. **Understanding Ammonium Salts**:
Ammonium salts are compounds that contain the ammonium ion (NH4+). Common examples include ammonium chloride (NH4Cl), ammonium sulfate ((NH4)2SO4), etc.

2. **Heating Ammonium Salts**:
When ammonium salts are heated, they can decompose to release ammonia gas. However, this is not the only condition under which ammonia can be liberated.

3. **Reaction with Alkali**:
Ammonium salts react with alkalis (such as sodium hydroxide, NaOH) to produce ammonia. For example, when ammonium chloride reacts with sodium hydroxide, the reaction can be represented as:
\[ NH4Cl + NaOH \rightarrow NaCl + NH3 + H2O \]
Here, ammonia (NH3) is released.

4. **Heating with Sulfuric Acid**:
When ammonium salts are heated with sulfuric acid (H2SO4), they do not liberate ammonia directly. Instead, they may form ammonium sulfate or other products, depending on the specific salt and conditions.

5. **Heating Alone**:
Simply heating ammonium salts may not always lead to the liberation of ammonia gas unless specific conditions are met (e.g., decomposition at high temperatures).

6. **Reaction with Nitrous Acid**:
Ammonium salts can react with nitrous acid (HNO2) to release nitrogen gas (N2) and water, but this does not typically liberate ammonia.

7. **Conclusion**:
From the analysis, we can conclude that ammonium salts liberate ammonia when heated with caustic soda (sodium hydroxide). Therefore, the correct answer is:
**Heated with caustic soda.**

### Final Answer:
All ammonium salts liberate ammonia when heated with caustic soda (NaOH).

---