Which of the following compounds gives positive Lassaigne's test for nitrogen?
(i) Urea
(ii) Hydrazine
(iii) Phenylhydrazine
(iv) Azobenzene

Options

A. (i), (ii), (iii), (iv)
B. (i), (iii), (iv)
C. (i), (ii), (iii)
D. (ii), (iii), (iv)

Explanation

To determine which of the given compounds gives a positive Lassaigne's test for nitrogen, we need to understand the requirements for this test. The Lassaigne's test is used to detect the presence of nitrogen in organic compounds. For a compound to give a positive result, it must contain both carbon and nitrogen.

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
- The test involves fusing the organic compound with sodium metal, which leads to the formation of sodium cyanide (NaCN) if nitrogen is present in the compound. Therefore, both carbon and nitrogen must be present in the compound for a positive result.

2. **Analyzing Each Compound**:
- **(i) Urea (NH2CONH2)**:
- Urea contains both carbon (C) and nitrogen (N).
- Therefore, it will give a positive Lassaigne's test.

- **(ii) Hydrazine (N2H4)**:
- Hydrazine does not contain carbon; it is composed only of nitrogen and hydrogen.
- Thus, it will not give a positive Lassaigne's test.

- **(iii) Phenylhydrazine (C6H7N3)**:
- Phenylhydrazine contains both carbon (from the phenyl group) and nitrogen.
- Therefore, it will give a positive Lassaigne's test.

- **(iv) Azobenzene (C12H10N2)**:
- Azobenzene contains carbon and nitrogen in its structure.
- Therefore, it will also give a positive Lassaigne's test.

3. **Conclusion**:
- The compounds that give a positive Lassaigne's test for nitrogen are:
- (i) Urea
- (iii) Phenylhydrazine
- (iv) Azobenzene

### Final Answer:
The compounds that give a positive Lassaigne's test for nitrogen are (i) Urea, (iii) Phenylhydrazine, and (iv) Azobenzene.