In Lassaigne's test for nitrogen, a blue colour is formed, which is\

Question

Professor PC Thomas Classes · Answer

Blue colour is ferric ferrocyanide $6 \mathrm{NaCN}+\mathrm{FeSO}_{4} ightarrow \mathrm{Na}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}ight]+\mathrm{Na}_{2} \mathrm{SO}_{4}$ $\left.4 \mathrm{Fe}^{3+}+3 \mathrm{Fe}(\mathrm{CN})_{6}ight]^{4-} ightarrow \mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}ight]_{3}$\