Assertion: Benzene diazonium chloride does not give tests for nitrogen.
Reason: `N_(2)` gas lost during heating.

Explanation

To solve the question, we need to analyze the assertion and the reason given:

**Assertion:** Benzene diazonium chloride does not give tests for nitrogen.
**Reason:** N₂ gas is lost during heating.

### Step-by-Step Solution:

1. **Understanding Benzene Diazonium Chloride:**
- Benzene diazonium chloride (C₆H₅N₂Cl) is a compound that contains a diazonium group (-N₂⁺) attached to a benzene ring.

2. **Testing for Nitrogen:**
- Tests for nitrogen typically involve detecting the presence of nitrogen gas (N₂). Common tests include the reaction of nitrogen-containing compounds with certain reagents that can indicate the presence of nitrogen.

3. **Behavior of Benzene Diazonium Chloride upon Heating:**
- When benzene diazonium chloride is heated, it undergoes decomposition. This process releases nitrogen gas (N₂) as a byproduct:
\[ C_6H_5N_2Cl \rightarrow C_6H_5Cl + N_2 \uparrow \]
- The nitrogen gas produced escapes into the atmosphere.

4. **Conclusion on the Assertion:**
- Since benzene diazonium chloride decomposes to release nitrogen gas upon heating, it does not retain nitrogen in a form that can be tested. Therefore, it does not give a positive test for nitrogen.

5. **Conclusion on the Reason:**
- The reason provided states that N₂ gas is lost during heating, which is indeed correct. This loss of nitrogen gas explains why benzene diazonium chloride does not give tests for nitrogen.

6. **Final Evaluation:**
- Both the assertion and the reason are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and the reason are correct, and the reason supports the assertion.

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