Lassaigne's test for the detection of nitrogen will fail in case of `:`

Options

A. `NH_(2)CONH_(2)`
B. `CH_(3)CONH_(2)`
C. `NH_(2)NH_(2)`
D. `C_(6)H_(5)NH_(2)`

Answer

To determine which compound Lassaigne's test for the detection of nitrogen will fail in, we need to analyze each option based on the presence of carbon, as the test requires carbon to produce sodium cyanide (NaCN) from the reaction with sodium.

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
- Lassaigne's test is used to detect the presence of nitrogen, sulfur, and halogens in organic compounds.
- A small piece of sodium metal is heated with the organic compound in a fusion tube. Sodium reacts with the elements in the compound to form ionic salts.

2. **Reactions Involved**:
- Sodium reacts with nitrogen to form sodium cyanide (NaCN).
- If sulfur is present, it forms sodium sulfide (Na2S).
- If halogens are present, sodium halides are formed.

3. **Analyzing Each Compound**:
- **Option A: Urea (NH2CONH2)**:
- Contains both nitrogen and carbon.
- Can produce sodium cyanide (NaCN).
- **Conclusion**: Lassaigne's test can be performed.

- **Option B: Acetamide (CH3CONH2)**:
- Contains both nitrogen and carbon.
- Can also produce sodium cyanide (NaCN).
- **Conclusion**: Lassaigne's test can be performed.

- **Option C: Hydrazine (NH2NH2)**:
- Contains nitrogen but does not contain carbon.
- Cannot produce sodium cyanide (NaCN) as there is no carbon present.
- **Conclusion**: Lassaigne's test will fail.

- **Option D: Aniline (C6H5NH2)**:
- Contains both nitrogen and carbon.
- Can produce sodium cyanide (NaCN).
- **Conclusion**: Lassaigne's test can be performed.

4. **Final Conclusion**:
- The only compound that will fail in Lassaigne's test for the detection of nitrogen is **Hydrazine (NH2NH2)**.

### Answer:
The correct option is **C: NH2NH2 (Hydrazine)**.