When a salt is treated with sodium hydroxide solution it gives gas $\mathrm{X}$. On passing gas $\mathrm{X}$ through reagent $\mathrm{Y}$ a brown coloured precipitate is formed. $\mathrm{X}$ and $\mathrm{Y}$ respectively, are

• A

  $\mathrm{X}=\mathrm{NH}_3$ and $\mathrm{Y}=\mathrm{HgO}$
• Correct answer
  B

  $\mathrm{X}=\mathrm{NH}_3$ and $\mathrm{Y}=\mathrm{K}_2 \mathrm{HgI}_4+\mathrm{KOH}$
• C

  $\mathrm{X}=\mathrm{NH}_4 \mathrm{Cl}$ and $\mathrm{Y}=\mathrm{KOH}$
• D

  $\mathrm{X}=\mathrm{HCl}$ and $\mathrm{Y}=\mathrm{NH}_4 \mathrm{Cl}$

Solution

$\mathrm{NH}_4^{+}+\mathrm{NaOH} \longrightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{NH}_3 \uparrow$

$\mathrm{NH}_3$ is identify by $\mathrm{K}_2\left[\mathrm{HgI}_4\right]+\mathrm{KOH}$

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