A student wants to prepare a saturated solution of ${\text{Ag}}^{\text{+}}$  ion. He has got only three samples  $\text{AgCl}\left({\text{K}}_{\text{sp}}{\text{=1.8×10}}^{-\text{10}}\right)$, $\text{AgBr}\left({\text{K}}_{\text{sp}}{\text{=5×10}}^{-\text{13}}\right)$  and  ${\text{Ag}}_{\text{2}}{\text{CrO}}_{\text{4}}\left({\text{K}}_{\text{sp}}{\text{=2.4×10}}^{-\text{12}}\right)$. Which compound he should use to have maximum  $\left[{\text{Ag}}^{\text{+}}\right]$: