In lassaigne's test a blue colour is obtained if the organic compound contains nitrogen. The blue colour is due to

Options

A. `K_(4)[Fe(CN)_(6)]`
B. `Fe_(4)[Fe(CN)_(6)]_(3)`
C. `Na_(3)[Fe(CN)_(6)]`
D. `Cu_(2)[Fe(CN)_(6)]`

Answer

To solve the question regarding the blue color obtained in Lassaigne's test when nitrogen is present in an organic compound, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
- Lassaigne's test, also known as the sodium fusion test, is used to detect the presence of halogens, nitrogen, and sulfur in organic compounds.

**Hint**: Remember that Lassaigne's test is primarily a qualitative analysis method for detecting specific elements in organic compounds.

2. **Reaction with Sodium**:
- When an organic compound containing nitrogen is fused with sodium, sodium reacts with nitrogen to form sodium cyanide (NaCN).

**Hint**: Focus on the fact that sodium acts as a reducing agent and reacts with nitrogen to form a specific compound.

3. **Formation of Sodium Ferrocyanide**:
- The sodium cyanide (NaCN) formed then reacts with ferrous sulfate (FeSO4) to produce sodium ferrocyanide (NaFe(CN)6).

**Hint**: Keep in mind the role of ferrous ions in the reaction and how they interact with sodium cyanide.

4. **Formation of Prussian Blue**:
- The sodium ferrocyanide can further react with ferric ions (Fe³⁺) present in the solution to form ferric ferrocyanide, which is known as Prussian blue (Fe₄[Fe(CN)₆]₃).

**Hint**: Remember that the presence of ferric ions is crucial for the formation of the characteristic blue color.

5. **Conclusion**:
- The blue color observed in Lassaigne's test when nitrogen is present is due to the formation of ferric ferrocyanide (Prussian blue).

**Hint**: Conclude by linking the final product (ferric ferrocyanide) to the observed color change in the test.

### Final Answer:
The blue color in Lassaigne's test, when nitrogen is present in the organic compound, is due to the formation of ferric ferrocyanide (Prussian blue).