Appearance of blood red colour, on treatment of the sodium fusion extract of an organic compound with $$FeSO_4$$ in presence of concentrated $$H_2SO_4$$ indicates the presence of element/s

We need to determine which element(s) are indicated by a blood red colour when the sodium fusion extract is treated with $$FeSO_4$$ and concentrated $$H_2SO_4$$.

Understand the Lassaigne (sodium fusion) test.

In the sodium fusion test, the organic compound is fused with sodium metal. During fusion:

- Nitrogen in the compound forms $$NaCN$$ (sodium cyanide)

- Sulphur forms $$Na_2S$$ (sodium sulphide)

- If both N and S are present, $$NaSCN$$ (sodium thiocyanate) is formed

Describe the reaction that produces blood red colour.

When $$FeSO_4$$ is added to the sodium fusion extract containing $$NaSCN$$:

$$FeSO_4 + 2NaSCN \rightarrow Fe(SCN)_2 + Na_2SO_4$$

In the presence of concentrated $$H_2SO_4$$ (which oxidises $$Fe^{2+}$$ to $$Fe^{3+}$$):

$$Fe^{3+} + SCN^- \rightarrow [Fe(SCN)]^{2+}$$

The ferric thiocyanate complex $$[Fe(SCN)]^{2+}$$ has a characteristic blood red colour.

Identify the elements.

The formation of thiocyanate ($$SCN^-$$) requires BOTH nitrogen (for the CN part) and sulphur (for the S part). Therefore, the blood red colour indicates the presence of both nitrogen and sulphur in the organic compound.

Note: If only nitrogen were present (without sulphur), the test with $$FeSO_4$$ would give Prussian blue colour (from ferric ferrocyanide), not blood red.

The correct answer is Option (3): N and S.