Question

In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with Fe³⁺ due to the formation of-

(1) NaSCN

(2) [Fe(CN)₅ NOS]^4-

(3) [Fe(SCN)]²⁺

(4) Fe₄[Fe(CN₆)]₃.xH₂O

Answer 1

Correct option is (3) [Fe(SCN)]²⁺

In case nitrogen and sulphur both are present in an organic compound, sodium thiocyanate is formed, it give blood red colour and no prussian blue since there are no free cyanide lons.

Na + C + N + S → NaSCN

Fe⁺³ + SCN\(^\Theta\) → [Fe(SCN)]²⁺ (Blood red)