When a salt is treated with sodium hydroxide solution it gives gas \( X \). On passing gas \( X \) through reagent \( Y \) a brown coloured precipitate is formed. \( X \) and \( Y \) respectively, are:
\( X = \mathrm{NH_4Cl} \) and \( Y = \mathrm{KOH} \)
\( X = \mathrm{HCl} \) and \( Y = \mathrm{NH_4Cl} \)
\( X = \mathrm{NH_3} \) and \( Y = \mathrm{K_2HgI_4} + \mathrm{KOH} \)
\( X = \mathrm{NH_3} \) and \( Y = \mathrm{HgO} \)