Addition of sodium thiosulphate solution to a solution of silver nitrate gives $X$ as a white precipitate, which is insoluble in water but soluble in excess thiosulphate solution to give $Y$. On boiling in water, $Y$ gives $Z$. $X$, $Y$, and $Z$ respectively are:

• A
  $Ag_{2}S_{2}O_{3}$, $Na_{3}[Ag(S_{2}O_{3})_{2}]$, $Ag_{2}S$
• B
  $Ag_{2}SO_{4}$, $Na[Ag(S_{2}O_{3})_{2}]$, $Ag_{2}S_{2}$
• C
  $Ag_{2}S_{2}O_{3}$, $Na_{5}[Ag(S_{2}O_{3})_{3}]$, $AgS$
• D
  $Ag_{2}SO_{3}$, $Na_{3}[Ag(S_{2}O_{3})_{2}]$, $Ag_{2}O$