[vernii]

Why don't colligative properties of solutions depend upon the size of the solute particles as it may create difference in the area of surface of solution; i mean number of particles covering it!!

[Corribus]

For real solutions the properties in question certainly depend on the chemical nature of the solute (charge density, size, etc.). However most of the simple theories to describe such effects are relevant only for ideal solutions, where the properties of the solution are (approximately) neglected. In this limit only the concentration of solute particles matters, and mixing is entirely entropic in nature.