Which one of the following $ 1.0 \times 10^{-3}$ molal aqueous solutions has the highest boiling point ?

Question

$\begin {array} {1 1} (1)\;Aluminium\: (III) \: Chloride & \quad (2)\;Lead \: (II) \: Nitrate \\ (3)\;Sodium\: Chloride & \quad (4)\;Magnesium\: Nitrate \end {array}$