Properties of dilute solutions of non-volatile solutes whose values depend upon the concentration and number of solute particles in the solution but not on the individuals identity of the solute. These can be known as colligative pressure. Various colligative properties are
(i) Relative lowering of vapour pressure
(ii) Elevation in boiling point
(iii) Depression in freezing point
(iv) Osmotic pressure
So; optical activity is not a colligative property.