Which of the following aqueous solutions, will have the highest boiling point?

$2.0\text{ M K}_2\text{SO}_4$

The correct answer is Option (4) → $2.0\text{ M K}_2\text{SO}_4$ ##

The elevation in boiling point is a colligative property that depends on the impurity present.

$\text{K}_2\text{SO}_4 \rightarrow 2\text{K}^+ + \text{SO}_4^{2-}$

$i = 3 \text{ (}i = \text{van't Hoff factor)}$

When higher impurities are present in a solution, the boiling point of solution increases, which is directly proportional to molality of the solute and van't Hoff factor of the solution.