Which of the following compounds will not give Lassaigne's test for nitrogen ?

Options

A. `NH_(2)NH_(2)`
B. `C_(6)H_(5)NHNH_(2)`
C. phN=Nph
D. `NH_(2)CONH_(2)`

Explanation

To determine which of the given compounds will not give Lassaigne's test for nitrogen, we need to understand the principle behind the test. Lassaigne's test is used to detect the presence of nitrogen in organic compounds. The key point is that for a compound to give a positive Lassaigne's test, it must contain carbon.

Let's analyze each option step by step:

### Step 1: Analyze the first compound (NH2NH2)
- **Compound**: NH2NH2 (Hydrazine)
- **Carbon Content**: This compound contains no carbon atoms.
- **Conclusion**: Since there is no carbon present, this compound will not give a Lassaigne's test for nitrogen.

### Step 2: Analyze the second compound (C6H5NH2NH2)
- **Compound**: C6H5NH2NH2 (Phenylhydrazine)
- **Carbon Content**: This compound contains carbon atoms (C6H5 indicates a phenyl group).
- **Conclusion**: Since it contains carbon, this compound will give a Lassaigne's test for nitrogen.

### Step 3: Analyze the third compound (Ph-N=N-Ph)
- **Compound**: Ph-N=N-Ph (Diphenylhydrazine)
- **Carbon Content**: This compound also contains carbon atoms (two phenyl groups).
- **Conclusion**: Since it contains carbon, this compound will give a Lassaigne's test for nitrogen.

### Step 4: Analyze the fourth compound (NH2CNH2)
- **Compound**: NH2CNH2 (Urea)
- **Carbon Content**: This compound contains carbon (the carbon atom is present in the -CNH2 group).
- **Conclusion**: Since it contains carbon, this compound will give a Lassaigne's test for nitrogen.

### Final Conclusion:
The only compound that does not give Lassaigne's test for nitrogen is **option 1: NH2NH2**.

### Summary of the Answer:
**Correct Answer**: Option 1 (NH2NH2)