JEE Main 2023 · 6 April · evening · Single correct · +4 / −1
Element not present in Nessler's reagent is :
- (a) I
- (b) N
- (c) K
- (d) Hg
Answer and solution
Answer (b) N
Solution
Chemistry ma’am · 4 steps
Write the formula of Nessler's reagent first, then check which element is missing from it.
- What the reagent is. Nessler's reagent is potassium tetraiodomercurate(II), K₂[HgI₄], dissolved in KOH solution. It is made by adding excess KI to HgCl₂.
HgCl₂ + 4KI → K₂[HgI₄] + 2KCl
- Elements present. The reagent contains K, Hg and I, plus O and H from the alkali. Nitrogen does not appear anywhere in it.
- Where N comes in. Nitrogen comes from the NH₄⁺ ion being tested. With NH₃, the reagent gives a brown precipitate of the iodide of Millon's base, HgO.Hg(NH₂)I. Only this product contains N.
- So. The element not present in Nessler's reagent is N, option (b).
The idea to keep. Nessler's reagent is alkaline K₂[HgI₄]. It detects nitrogen as ammonium. The N belongs to the sample and the brown precipitate, never to the reagent.
Answer from the NTA final answer key. Solution by PrepWiser.