On passing a gas, 'X', through Nessler's regent, a brown precipitate is obtained. The gas 'X' is

Solution

Chemistry ma’am · 3 steps

Nessler's reagent is the classic test for ammonia, so a brown precipitate points straight to NH₃.

1. Know the reagent. Nessler's reagent is an alkaline solution of potassium tetraiodomercurate(II), K₂[HgI₄] in KOH. In salt analysis it is used to detect NH₄⁺: you heat the salt with NaOH and pass the gas given off through the reagent.
2. Reaction with ammonia. Ammonia reacts with [HgI₄]²⁻ in the alkaline solution. It forms a brown precipitate called the iodide of Millon's base, HgO·Hg(NH₂)I.

   2K₂[HgI₄] + NH₃ + 3KOH → HgO·Hg(NH₂)I v + 7KI + 2H₂O

3. So. The gas that gives a brown precipitate with Nessler's reagent is ammonia, option (c).

The idea to keep. Link each gas to its own test: NH₃ gives a brown precipitate with Nessler's reagent, CO₂ turns lime water milky, and H₂S turns lead acetate paper black.

Answer from the NTA final answer key. Solution by PrepWiser.