The Lassaigne's extract is boiled with dil. `HNO_(3)` before testing for halogens because

Options

A. Silver halides are soluble in `HNO_(3)`
B. `Na_(2)S` and NaCN are decomposed by `HNO_(3)`
C. `Ag_(2)S` is soluble in `HNO_(3)`
D. `AgCN` is soluble in `HNO_(3)`

Answer

To answer the question, "The Lassaigne's extract is boiled with dilute HNO3 before testing for halogens because," we need to analyze the purpose of this step in the context of the Lassaigne's test.

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
- Lassaigne's test is a qualitative analysis method used to detect the presence of nitrogen, sulfur, and halogens in organic compounds.
- In this test, sodium metal is fused with the organic compound, converting elements into their ionic forms.

2. **Formation of Salts**:
- During the fusion, sodium reacts with nitrogen to form sodium cyanide (NaCN), with sulfur to form sodium sulfide (Na2S), and with halogens to form sodium halides (NaX, where X is a halogen).

3. **Preparation of Lassaigne's Extract**:
- The fused mass is then boiled with distilled water to extract the formed salts, resulting in the Lassaigne's extract.

4. **Need for Dilute HNO3**:
- Before testing for halogens, the Lassaigne's extract is boiled with dilute nitric acid (HNO3).
- The purpose of this step is to decompose sodium cyanide (NaCN) and sodium sulfide (Na2S) present in the extract.

5. **Decomposition Reactions**:
- When NaCN is treated with dilute HNO3, it produces hydrogen cyanide (HCN) gas and sodium nitrate (NaNO3):
\[ \text{NaCN} + \text{HNO}_3 \rightarrow \text{HCN} + \text{NaNO}_3 \]
- When Na2S is treated with dilute HNO3, it produces hydrogen sulfide (H2S) gas and sodium nitrate (NaNO3):
\[ \text{Na}_2\text{S} + 2\text{HNO}_3 \rightarrow \text{H}_2\text{S} + 2\text{NaNO}_3 \]

6. **Importance of Removing Interfering Compounds**:
- By boiling the extract with dilute HNO3, we eliminate the interference from HCN and H2S, which could otherwise react with silver nitrate (AgNO3) used for testing halogens.

7. **Testing for Halogens**:
- After boiling with HNO3, the solution is cooled, and silver nitrate is added. The presence of halogens is indicated by the formation of precipitates:
- Chloride (Cl-) forms a white precipitate (AgCl).
- Bromide (Br-) forms a cream precipitate (AgBr).
- Iodide (I-) forms a yellow precipitate (AgI).

### Conclusion:
The correct reason for boiling Lassaigne's extract with dilute HNO3 before testing for halogens is that it decomposes sodium cyanide and sodium sulfide, preventing interference in the subsequent halogen detection.