Which solution has the lowest boiling point at standard pressure? (a) 0.40 M KCl(aq)
(b) 0.20 M K2SO4(aq)
(c) 0.10 M K3PO4(aq)
(d) pure water

(d) pure water

Explanation:

A colligative property of solvents as water is the elevation of boiling point that describes how the presence of solutes in a solvent produce the increase in boiling point regard to the boiling point of the pure solvent.

In the problem, there are 3 solution that contains an amount of solute dissolved that will increase the boiling point of this solution but there is a solution that is just pure water. As the presence of solutes increases the boiling point, the pure water is the solution that has the lowest boiling point: