Question

Lassaigne’s extract of thiourea, $SC(N{H}_2{)}_2$ is boiled with ferrous sulphate and then acidified with $HCl,$ the colour of the resulting solution will be

Answer 1

$\text{Lassaigne's test for thiourea}$

When nitrogen and sulphur both are present in an organic compound, in Lassaigne’s test sodium thiocyanate is formed. It gives blood red colour when treated with $F{e}^{3+}$ salt. This $F{e}^{3+}$ salt gets formed due to the oxidation of ferrous ions on boiling with acid.

$Na+C+N+S\to NaSCN$

$F{e}^{3+}+3SC{N}^{-}\to Fe(SCN{)}_3$
Blood red

Since thiourea $\left(SC\right(N{H}_2{)}_2)$ contains both sulphur and nitrogen. So, when Lassaigne’s extract of thiourea is boiled with ferrous sulphate and then acidified with $HCl,$ the colour of the resulting solution will be red.

So, the correct answer is option (d).