Dinitrogen gas is evolved when sodium nitrite is heated below 500 degree centigrade :

Options

A. alone
B. with ammonium chloride
C. with ammonium hydroxide
D. with potassium nitrate

Explanation

To solve the question regarding the evolution of dinitrogen gas when sodium nitrite is heated below 500 degrees centigrade, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**: We need to identify the conditions under which dinitrogen gas (N₂) is evolved from sodium nitrite (NaNO₂). The question specifies that this must occur below 500 degrees centigrade.

2. **Heating Sodium Nitrite Alone**:
- When sodium nitrite (NaNO₂) is heated alone, the reaction is:
\[ 2 \text{NaNO}_2 \rightarrow \text{Na}_2\text{O} + \frac{3}{2} \text{O}_2 + \text{N}_2 \]
- This reaction requires a temperature of at least 800 degrees centigrade to produce nitrogen gas. Therefore, heating sodium nitrite alone does not meet the condition of being below 500 degrees centigrade.

3. **Heating Sodium Nitrite with Ammonium Chloride**:
- Next, we consider the reaction of sodium nitrite with ammonium chloride (NH₄Cl):
\[ \text{NaNO}_2 + \text{NH}_4\text{Cl} \rightarrow \text{NaCl} + \text{N}_2 + 2 \text{H}_2\text{O} \]
- This reaction occurs at temperatures below 500 degrees centigrade and produces nitrogen gas.

4. **Checking Other Options**:
- We can also consider the reactions with ammonium hydroxide (NH₄OH) and potassium nitrate (KNO₃), but based on the information provided, we find that these do not yield nitrogen gas under the specified conditions.

5. **Conclusion**:
- The only viable reaction that produces dinitrogen gas when sodium nitrite is heated below 500 degrees centigrade is with ammonium chloride. Therefore, the correct answer is:
\[ \text{Option B: Sodium nitrite with ammonium chloride.} \]

### Final Answer:
**Option B is correct.**

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