For which of the following compounds will Lassaigne's test for nitrogen fail ?

Options

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

Explanation

To determine for which of the following compounds Lassaigne's test for nitrogen will fail, we need to understand the principles behind Lassaigne's test. This test is used to detect the presence of nitrogen in organic compounds by converting nitrogen into sodium cyanide (NaCN) when the compound is heated with sodium.

### Step-by-Step Solution:

1. **Identify the Compounds**: The first step is to identify the compounds given in the question. Let's assume we have the following compounds:
- A) Urea (NH2CONH2)
- B) Acetamide (CH3CONH2)
- C) Ammonium chloride (NH4Cl)
- D) Benzene (C6H6)

2. **Understanding Lassaigne's Test**: Lassaigne's test involves heating the organic compound with sodium. If nitrogen is present, it will react with sodium to form sodium cyanide (NaCN). The presence of NaCN indicates a positive result for nitrogen.

3. **Analyze Each Compound**:
- **Urea (NH2CONH2)**: When urea reacts with sodium, it will produce NaCN. Therefore, Lassaigne's test will be positive.
- **Acetamide (CH3CONH2)**: This compound also contains nitrogen and will react with sodium to form NaCN, resulting in a positive test.
- **Ammonium chloride (NH4Cl)**: This compound contains nitrogen and will react with sodium to form NaCN, hence it will also give a positive result.
- **Benzene (C6H6)**: Benzene does not contain nitrogen. When heated with sodium, it will not form NaCN. Therefore, Lassaigne's test will fail for benzene.

4. **Conclusion**: The compound for which Lassaigne's test for nitrogen will fail is benzene (C6H6).

### Final Answer:
The correct answer is **Benzene (C6H6)**.