Question

an aqueous solution freezes at -1.5C.Calculate the boiling point of the solution if the Kf is 1.86 and Kb is 0.51

Answer 1

I suppose we assume the solute is a non-volatile one and does not ionize.
dTfreeze = Kf*m
dT = 1.5, you know Kf, solve for molality.

Then dTboiling = Kb*m
You know Kb and m, solve for dT and add it to 100 C.

Post your work if you get stuck.

Answer 2

Why to add 100