In the detection of nitrogen in an organic compound The appearance of Prussian blue colouration is due to the formation of:

Explanation

In the Lassaigne's test, nitrogen in an organic compound forms sodium cyanide (NaCN) when fused with Na. On adding Fe²⁺ ions, it reacts with CN⁻ to form ferric ferrocyanide (Fe₄[Fe(CN)₆]₃). This compound is Prussian blue, giving the characteristic blue coloration.