On adding ${\mathrm{AgNO}}_3$ solution to a solution of $\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]\mathrm{CI}$ the percentage of total chloride ion precipitated is :

Since only one chlorine atom is ionized from the four-chlorine atom the percentage of total chloride ion  precipitated is 25 %.

$\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{C}}_3\right]\mathrm{Cl}$

$\mathrm{AgCl} \mathrm{\%}$ of $\mathrm{CI}$ precipitated  $=\frac{1}{4}\times 10$

$\mathrm{AgCl} \mathrm{\%}$ of $\mathrm{CI}$ precipitated   = 25 %

Hence correct option is D.