# Which of the following compound will give blood red colour while doing the Lassigne's test for N?

(a) $(NH_2)_2C=O$
(b) $H_2N(C_6H_4)SO_3H$
(c) $C_6H_5SO_2H$
(d) $CHCl_3$

Answer: $H_2N(C_6H_4)SO_3H$

$H_2N(C_6H_4)SO_3H$ contains N, S and C. During fusion with sodium metal, it will form
$NaCNS$ which gives a blood red colouration with $Fe^{3+}$ ions.
$Na + N + C + S \xrightarrow{Fuse} Na^+CNS^-$
$Fe^{3+} + 3CNS^- \longrightarrow Fe(CNS)_3$ Ferric sulphocyanide (Blood red colouration)