In Lassaigne’s test, which element is revealed by the formation of a precipitate of Prussian blue on heating part of the solution with iron (II) sulphate solution?

Correct option is D

The correct answer is: (d) Nitrogen
Explanation:
· Lassaigne’s test is used to detect nitrogen, sulphur, and halogens in an organic compound by converting them into inorganic soluble forms (NaCN, Na2S, NaX).
· When an organic compound containing nitrogen is fused with sodium metal, it forms sodium cyanide (NaCN).
· The Lassaigne extract (LE) containing NaCN is then treated with ferrous sulphate (FeSO₄) and heated.
· On addition of ferric ions and acidification, the formation of Prussian Blue (ferric ferrocyanide, Fe₄[Fe(CN)₆]₃) confirms the presence of nitrogen.
Information Booster:
· Formation of sodium cyanide during fusion is the key step enabling nitrogen detection.
· The reaction sequence involves ferrocyanide formation, which then reacts with ferric ions to produce the blue-colored precipitate.
Additional Knowledge (Incorrect Options):
Carbon (Option a)
· Carbon does not give any characteristic color or precipitate in Lassaigne’s test.
Hydrogen (Option c)
· Hydrogen is not detected using Lassaigne’s extract methods.
Oxygen (Option b)
· Oxygen has no specific qualitative test in organic analysis.