Correct choice is (a) Colligative properties
Easy explanation: Colligative properties are set of four properties. This set of properties purely depends on the number of solute particles present in the solution/solvent, independent of the nature of the particles with respect to the solution/solvent. The properties are 1.) Relative lowering of vapor pressure, 2.) Elevation in boiling point, 3.) Depression in freezing point and 4.) Osmotic pressure.