The Prussian blue colour obtained during the test of nitrogen by Lassaigne's test is due to the formation of-

The Lassaigne's extract is boiled with a concentration HNO₃ while testing for halogens. By doing so it:

1. Helps in the precipitation of AgCl.

2. Increases the solubility product of AgCl.

3. Increases the concentration of NO₃^- ions.

4. Decomposes Na₂S and NaCN, if formed.