In Lassaigne's test for the detection of nitrogen in an organic compound, the appearance of a Prussi — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

During Lassaigne's test, sodium cyanide formed reacts with $FeSO_4$ to form sodium hexacyanoferrate(II). Upon acidification and addition of $Fe^{3+}$ (from $FeCl_3$), it forms Iron(III) hexacyanoferrate(II), $Fe_4[Fe(CN)_6]_3$, which has a Prussian blue color.