JEE Chemistry 2023 Question with Solution

Given: The question asks which element is not present in Nessler’s reagent.

Find: The element absent from the composition of the reagent.

Nessler’s reagent is potassium tetraiodomercurate(II) with formula $K_2[HgI_4]$.

From this formula, the elements present are K, Hg, and I.

Therefore, N is not present in Nessler’s reagent.

The correct option is B.

Given: Nessler's reagent is used for detection of ammonia $NH_3$ or ammonium ions $NH_4^+$.

Find: Which listed element is not a constituent of the reagent itself.

Nessler's reagent is prepared from compounds such as KI, HgCl_2, and KOH, and its alkaline reagent composition is written as $K_2[HgI_4]$.

So the reagent contains:

• K = potassium
• Hg = mercury
• I = iodine

Although the reagent is used to detect nitrogen-containing species, nitrogen is not part of the reagent formula.

Therefore, the correct option is B.