A colorless aqueous solution contains nitrates of two metals, \(\mathbf{X}\) and
\(\mathbf{Y}\). When it was added to an aqueous solution of \(\mathrm{NaCl}\), a
white precipitate was formed. This precipitate was found to be partly soluble
in hot water to give a residue \(\mathbf{P}\) and a solution \(\mathbf{Q}\). The
residue \(\mathbf{P}\) was soluble in aq. \(\mathrm{NH}_{3}\) and also in excess
sodium thiosulfate. The hot solution \(\mathbf{Q}\) gave a yellow precipitate
with KI. The metals \(\mathbf{X}\) and \(\mathbf{Y}\), respectively, are [Adv.
2020](a) \(\mathrm{Ag}\) and \(\mathrm{Pb}\)
(b) \(\mathrm{Ag}\) and \(\mathrm{Cd}\)
(c) \(\mathrm{Cd}\) and \(\mathrm{Pb}\)
(d) \(\mathrm{Cd}\) and \(\mathrm{Zn}\)