In which of the following compounds, nitrogen cannot be tested by Lassaigne's test?

Options

A. `CH_3CONH_2`
B. `NH_2.NH_2H_2O`
C. `C_6H_5NH_2`
D. `C_6H_5NO_2`

Answer

To determine in which of the following compounds nitrogen cannot be tested by Lassaigne's test, we need to understand the principles behind the test and the nature of the compounds involved.

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
Lassaigne's test is a qualitative analysis method used to detect the presence of nitrogen in organic compounds. The test involves the fusion of the organic compound with sodium metal, which helps to convert nitrogen into sodium cyanide (NaCN).

2. **Requirement for Lassaigne's Test**:
For nitrogen to be detected using Lassaigne's test, the organic compound must contain carbon. This is because the formation of sodium cyanide, which is necessary to indicate the presence of nitrogen, requires carbon to be present in the compound.

3. **Analyzing the Compounds**:
We need to examine the given compounds to see which one does not contain carbon. If a compound lacks carbon, it cannot form cyanide ions (CN⁻), and therefore nitrogen cannot be tested.

4. **Identifying the Compound**:
Let's consider the options provided:
- If one of the options is NiH₂ (Nickel hydride), it does not contain carbon.
- Other options should be checked for the presence of carbon.

5. **Conclusion**:
The compound that does not contain carbon (like NiH₂) cannot be tested for nitrogen using Lassaigne's test because it cannot form sodium cyanide.

### Final Answer:
The compound in which nitrogen cannot be tested by Lassaigne's test is **NiH₂**.

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