Q27 / 160 · AP EAMCET 2020 (21 Sep Shift 2) · Chemistry

A pungent smelling gas \(A\) gives dense white fumes with conc. \(\mathrm{HCl}\). When \(A\) reacts with alkaline solution of a colourless reagent \(B\), a reddish-brown precipitate \(C\) is formed. The compounds \(A, B, C\) respectively are

  • A
    \(\mathrm{NO}_2, \mathrm{NaOH},\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{NO}\right]^{2+}\)
  • B
    \(\mathrm{NH}_3, \mathrm{NaOH}, \mathrm{K}_2 \mathrm{Hgl}_4\)
  • Correct answer
    C
    \(\mathrm{NH}_3, \mathrm{~K}_2 \mathrm{Hgl}_4, \mathrm{NH}_2, \mathrm{HgO}, \mathrm{Hgl}\)
  • D
    \(\mathrm{Cl}_2\), Sodium nitroprusside, \(\left[\mathrm{Na}_2 \mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right]\)

Solution

Ammonia gas reacts with hydrogen chloride gas to form dense white fumes of ammonium chloride. This is used as a test to detect the presence of ammonia gas as per the reaction. \(\mathrm{NH}_3(g)+\mathrm{HCl}(g) \longrightarrow \mathrm{NH}_4 \mathrm{Cl}(s)\) Nessler's reagent is a solution containing \(\mathrm{K}_2 \mathrm{HgI}_4\) and \(\mathrm{KOH}\). lodide and mercury ions react with ammonia under alkaline conditions to produce a reddish brown complex, iodide of million's base \(\left(\mathrm{H}_2 \mathrm{~N}-\mathrm{Hg}-\mathrm{O}-\mathrm{Hg}-\mathrm{I}\right)\) formed. Hence, the correct option is (c).

Hence, the correct answer is option: 'C'.

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