The covalent compound which does not give positive test in Lassaigne's test is

Options

A. 1,3-Dinitrobenzene
B. glycine
C. Urea
D. Hydroxyl amine

Answer

To determine which covalent compound does not give a positive test in Lassaigne's test, we need to analyze the given compounds based on their elemental composition, specifically looking for the presence of carbon and nitrogen. Lassaigne's test is used to detect the presence of nitrogen, sulfur, and halogens in organic compounds.

### Step-by-step Solution:

1. **Understand Lassaigne's Test**:
Lassaigne's test involves fusing an organic compound with sodium to form sodium cyanide (NaCN) if nitrogen is present. For a positive test, both carbon and nitrogen must be present in the compound.

2. **Analyze the Compounds**:
We have four compounds to consider:
- **A: 1,3-Dinitrobenzene**
- **B: Glycine (NH2CH2COOH)**
- **C: Urea (NH2CO)**
- **D: Hydroxylamine (NH2OH)**

3. **Check Each Compound for Carbon and Nitrogen**:
- **Compound A (1,3-Dinitrobenzene)**:
- Contains carbon (from the benzene ring) and nitrogen (from the nitro groups).
- **Conclusion**: Will give a positive test.

- **Compound B (Glycine)**:
- Contains carbon (from the carbon chain) and nitrogen (from the amino group).
- **Conclusion**: Will give a positive test.

- **Compound C (Urea)**:
- Contains carbon (from the carbonyl group) and nitrogen (from the amine groups).
- **Conclusion**: Will give a positive test.

- **Compound D (Hydroxylamine)**:
- Contains nitrogen (from the amine group) but does not contain carbon in a form that can react to form NaCN.
- **Conclusion**: Will NOT give a positive test.

4. **Final Decision**:
Based on the analysis, the compound that does not give a positive test in Lassaigne's test is **D: Hydroxylamine**.