The $K_{\mathrm{sp}}$ of $\mathrm{Ag}_{2} \mathrm{CrO}_{4}=1.2 \times 10^{-11} .$ What
concentration Ag $^{+}$ ion in aqueous solution will just fail to give a precipitate of $\mathrm{Ag}_{2} \mathrm{CrO}_{4}$ with a solution in which $\left[\mathrm{CrO}_{4}^{-2}\right]=3 \times 10^{-4} \mathrm{M} ?$
(a) $10^{-3} \mathrm{M}$
(b) $10^{-1} \mathrm{M}$
(c) $10^{-4} \mathrm{M}$
(d) $2 \times 10^{-4} \mathrm{M}$