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Which of the following is not a colligative property. which arises in systems when there is addition of solute?

(1) Lowering of vapour pressure

(2) Lowering of melting point

(3) Lowering of boiling point

(4) Increase of osmotic pressure

Colligative Properties:

These properties depend only on the number of solute particles in a solution, not on the identity or nature of the solute particles. The four main colligative properties are:

  1. Lowering of vapor pressure: When a non-volatile solute is added to a solvent, the vapor pressure of the solvent decreases because fewer solvent molecules are able to escape into the gas phase.
  2. Lowering of melting point: When a solute is added to a solvent, the freezing point of the solution is lower than that of the pure solvent (this is also called freezing point depression).
  3. Lowering of boiling point: The boiling point of a solution is higher than that of the pure solvent when a solute is added (this is called boiling point elevation).
  4. Osmotic pressure: The pressure required to stop the osmosis (movement of solvent through a semi-permeable membrane) is higher when solute particles are present.

Now, let’s examine the options:

  • (1) Lowering of vapor pressure: This is a colligative property, as it depends on the number of solute particles.
  • (2) Lowering of melting point: This is a colligative property, known as freezing point depression.
  • (3) Lowering of boiling point: This is also a colligative property, known as boiling point elevation.
  • (4) Increase of osmotic pressure: This is a colligative property that increases when more solute particles are added.

Final Answer:

All of the options listed are colligative properties, but since the question asks which one is NOT, the answer seems to involve a misunderstanding because all these properties are colligative. So, there’s no correct option in the current list that directly contradicts the definition of colligative properties. If you meant to ask about a non-colligative property, the answer would have to be something like color change or chemical reactivity, which depend on the nature of the solute.

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