In the Lassaigne's test for the detection of sulphur, the purple colour is due to the formation of

Options

A. `Na_(4) [Fe(CN)_(5) NOS]`
B. `Na_(3)[Fe(CN)_(5)S]`
C. `Na_(2)[Fe(CN)_(5)NOS]`
D. `Na_(3) [Fe(CN)_(6)]`

Explanation

**Step-by-Step Solution:**

1. **Understanding Lassaigne's Test**: Lassaigne's test is a qualitative analysis method used to detect the presence of certain elements in organic compounds, including sulfur.

2. **Formation of Sodium Sulfide**: When an organic compound containing sulfur is heated with sodium, sodium sulfide (Na2S) is formed. This is the first step in the test.

- **Reaction**:
\[ \text{Organic Compound (S)} + \text{Na} \rightarrow \text{Na}_2\text{S} + \text{other products} \]

3. **Reaction with Sodium Nitroprusside**: The next step involves the reaction of sodium sulfide (Na2S) with sodium nitroprusside (Na2[Fe(CN)5NO]). This reaction is crucial for detecting sulfur.

- **Reaction**:
\[ \text{Na}_2\text{S} + \text{Na}_2[\text{Fe(CN)}_5\text{NO}] \rightarrow \text{Na}_4[\text{Fe(CN)}_5\text{NOS}] + \text{other products} \]

4. **Formation of Purple Compound**: The product formed from the reaction between sodium sulfide and sodium nitroprusside is sodium tetranitroprusside sulfide (Na4[Fe(CN)5NOS]), which has a characteristic purple color.

5. **Conclusion**: The purple color observed in Lassaigne's test indicates the presence of sulfur in the organic compound, and the compound responsible for this color is sodium tetranitroprusside sulfide (Na4[Fe(CN)5NOS]).

**Final Answer**: The purple color in Lassaigne's test for the detection of sulfur is due to the formation of sodium tetranitroprusside sulfide (Na4[Fe(CN)5NOS]).

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