Which compound does not give positive test in Lassaigne's test for nitrogen ?

Options

A. Urea
B. Hydrazine
C. Azobenzene
D. Phenyl hydrazine

Explanation

To determine which compound does not give a positive test in Lassaigne's test for nitrogen, we need to understand the requirements for a positive test. Lassaigne's test is used to detect the presence of nitrogen, sulfur, or halogens in organic compounds. The test involves fusing the organic compound with sodium metal, which helps to form sodium salts of the elements present in the compound.

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
- Lassaigne's test is performed to check for the presence of nitrogen, sulfur, or halogens in a compound.
- The organic compound is fused with sodium metal in a fusion tube.

2. **Formation of Sodium Cyanide**:
- If nitrogen is present in the organic compound, it will react with sodium to form sodium cyanide (NaCN).
- The presence of carbon is also essential because the compound must contain both carbon and nitrogen to yield sodium cyanide.

3. **Boiling with Distilled Water**:
- After fusion, the product is boiled with distilled water to extract the sodium salts formed during the reaction.

4. **Identifying the Compounds**:
- We need to analyze the given options (A, B, C, D) to see which one does not contain carbon, as the absence of carbon will lead to a negative test for nitrogen.
- **Option A: Urea (NH2CONH2)** - Contains carbon (C) and nitrogen (N), so it gives a positive test.
- **Option B: Hydrazine (NH2NH2)** - Contains nitrogen but no carbon, so it will not give a positive test.
- **Option C: Aniline (C6H5NH2)** - Contains carbon and nitrogen, so it gives a positive test.
- **Option D: Phenylhydrazine (C6H5NHNH2)** - Contains carbon and nitrogen, so it gives a positive test.

5. **Conclusion**:
- The compound that does not give a positive test in Lassaigne's test for nitrogen is **Hydrazine (Option B)**, as it lacks carbon.

### Final Answer:
**Hydrazine (Option B) does not give a positive test in Lassaigne's test for nitrogen.**