# Formation of purple colour on the addition of sodium nitroprusside to sodium carbonate extract indicates the presence of

(a) $PO_4^{3-}$
(b) $SO_3^{2-}$
(c) $S^{2-}$
(d) $S_2O_3^{2-}$

Answer: $S^{2-}$

$Na[(CN)_5NO]$ (Sodium nitroprusside) $+ Na_2S \xrightarrow{\Delta} Na_4[(CN)_5NOS]$ (Sodium thionitroprusside, violet purple)