Which of the following is not a colligative property ?

ANS:D - none of these.

The correct answer is: none of these. All of the options listed—osmotic pressure, depression of freezing point, and lowering of vapor pressure—are colligative properties. Colligative properties are properties of solutions that depend solely on the number of solute particles present in the solution, regardless of the identity of the solute particles. These properties include osmotic pressure, depression of freezing point, lowering of vapor pressure, and elevation of boiling point. Therefore, all the properties listed—osmotic pressure, depression of freezing point, and lowering of vapor pressure—are colligative properties.