A colorless aqueous solution contains nitrates of two metals, $\mathrm{X}$ and $\mathrm{Y}$. 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 $\mathrm{P}$ and a solution $\mathrm{Q}$. The residue $\mathrm{P}$ was soluble in aq. ${\mathrm{NH}}_3$ and also in excess sodium thiosulfate. The hot solution $\mathrm{Q}$ gave a yellow precipitate with $\mathrm{KI}$. The metals $\mathrm{X}$ and $\mathrm{Y}$, respectively, are

• Correct answer
  A

  $\mathrm{Ag}$ and $\mathrm{Pb}$
• B

  $\mathrm{Ag}$ and $\mathrm{Cd}$
• C

  $\mathrm{Cd}$ and $\mathrm{Pb}$
• D

  $\mathrm{Cd}$ and $\mathrm{Zn}$

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