What are colligative properties?

Equimolal solutions of non-electrolytes in the same solvent have:

Colligative properties are used for the determination of:

Consider $0.1 \ M$ solutions of two solutes $X$ and $Y$. The solute $X$ behaves as a univalent electrolyte while the solute $Y$ dimerises in solution. Which of the following statements are correct regarding these solutions?
$(a)$ The boiling point of the solution of $X$ will be higher than that of $Y$
$(b)$ The osmotic pressure of the solution of $X$ will be higher than that of $Y$
$(c)$ The freezing point of the solution of $X$ will be lower than that of $Y$
$(d)$ The relative lowering of vapour pressure of both the solutions will be the same
Select the correct answer from the given options $:-$

Equimolar solutions in the same solvent have ...

Which among the following is $NOT$ a colligative property?