Here's why:

* Physical properties can be observed or measured without changing the chemical composition of the substance.

* Chemical properties describe how a substance reacts or changes its composition.

Colligative properties are based on the number of solute particles in a solution, not the chemical nature of the solute itself. They are dependent on the concentration of the solution, which is a physical property.

Here are some examples of colligative properties:

* Vapor pressure lowering: The presence of a solute lowers the vapor pressure of the solvent.

* Boiling point elevation: The boiling point of a solution is higher than that of the pure solvent.

* Freezing point depression: The freezing point of a solution is lower than that of the pure solvent.

* Osmotic pressure: The pressure required to prevent the flow of solvent across a semipermeable membrane.

These properties are not determined by the chemical reactions or transformations of the solute. They are simply a result of the solute particles affecting the physical behavior of the solvent.