Which of the following is a colligative property?

Osmotic pressure

The correct answer is option 2. Osmotic pressure.

Out of the listed options, only (2) Osmotic pressure is a colligative property.

Here's why:

• Colligative properties are solution properties that depend only on the number of solute particles in the solution, not their identity. These properties are largely independent of the specific chemical nature of the solute and solvent.
• Vapour pressure (1), freezing point (3), and boiling point (4) can all be affected by both the type and amount of solute and solvent present in a solution. They are not solely dependent on the number of solute particles.
• Osmotic pressure (2), on the other hand, arises due to the difference in concentration of solute particles across a semipermeable membrane. It directly relates to the number of solute particles present and is essentially independent of their type.

Therefore, only osmotic pressure meets the criteria of being a colligative property. The other options, while important solution properties, are influenced by factors beyond just the number of solute particles.