Question

Which of the following compound will give a blood red colour while doing Lassaigne's test?

• A. $(N{H}_2{)}_{2}CO$
• B. $N{H}_2{C}_6{H}_{4}S{O}_{3}H$
• C. $H_{2}S{O}_4$
• D. $CHC{l}_3$

Answer 1

The correct option is B $N{H}_2{C}_6{H}_{4}S{O}_{3}H$

When both N and S are present in an organic compound, it gives a blood red colour in Lassaigne's test.

$C+N+S+Na\to N{a}^{+}CN{S}^{-}$

$F{e}^{3+}+SC{N}^{-}⟶\left[Fe\right(SCN){]}^{2+}$

The compound $\left[Fe\right(SCN){]}^{2+}$ is responsible for the blood red colouration.