If the solubility product of $MgF_2$ at a certain temperature is $ 1.08 \times 10^{-10}$ , its solubility in mol $1^{-1}$ is:

Question

$\begin {array} {1 1} (1)\;1.04 \times 10^{-5} & \quad (2)\;7.3 \times 10^{-4} \\ (3)\;3.0 \times 10^{-5} & \quad (4)\;3.0 \times 10^{-4} \end {array}$