The solubility product of $\mathrm{AgCl}$ is $1.8\times 10^{-10}$ at 298 K. Its molar solubility in pure water (in $\mathrm{mol}{\mathrm{L}}^{-1}$) is closest to

1. A$1.3\times 10^{-5}\mathrm{M}$
2. B$1.8\times 10^{-10}\mathrm{M}$
3. C$9.0\times 10^{-11}\mathrm{M}$
4. D$6.7\times 10^{-6}\mathrm{M}$