The solution of a chemical compound $\mathrm{X}$ reacts with ${\mathrm{AgNO}}_3$, solution to form a white precipitate of$\mathrm{Y}$ which dissolves in ${\mathrm{NH}}_4\mathrm{OH}$ to give a complex $\mathrm{Z}$. When $\mathrm{Z}$is treated with dil. ${\mathrm{HNO}}_3$,$\mathrm{Y}$ reappears. The chemical compound $\mathrm{X}$ can be