Which of the following reagents turns white precipitate of  $\mathrm{AgCl}$ yellow?

A whitish AgCl precipitate that becomes yellow is ${\mathrm{Na}}_3{\mathrm{AsO}}_3$

$\mathrm{AgCl}\stackrel{\mathrm{Nal}}{⟶}$ $$\begin{gathered} \mathbf{AgI}\downarrow \text{; } \\ (\mathrm{yellow} \mathrm{PPt}) \end{gathered}$$

$3\mathrm{AgCl}+{\mathrm{AsO}}_3^{3-}⟶{\mathrm{Ag}}_3{\mathrm{AsO}}_3\downarrow +3{\mathrm{Cl}}^{-}$

Both (a) and (b) reagents turns white precipitate of $\mathrm{AgCl}$ yellow.