JEE Main 2025 Apr 7 Shift 1, Chemistry Q12: Analysis of Amines

The classical confirmatory test for ammonium ion involves two steps:

Step 1 (liberation of gas X): An ammonium salt warmed with NaOH liberates ammonia gas.

${\text{NH}}_4^{+}+{\text{OH}}^{-}\to {\text{NH}}_3\uparrow +{\text{H}}_2\text{O}$

Step 2 (confirmation with Nessler's reagent): Nessler's reagent is an alkaline solution of K${}_2$[HgI${}_4$]. It reacts with NH${}_3$ to give a brown (iodide of Millon's base) precipitate:

$2[{\text{HgI}}_4{]}^{2-}+{\text{NH}}_3+3{\text{OH}}^{-}\to [{\text{Hg}}_2\text{N}]\text{I}\cdot {\text{H}}_2\text{O}\downarrow +7{\text{I}}^{-}+2{\text{H}}_2\text{O}$

The brown precipitate is iodide of Millon's base.

$\therefore$ X = NH${}_3$, Y = K${}_2$HgI${}_4$ + KOH $\Rightarrow$ Option (2).