The dilute solutions of non-volatile solutes exhibit certain characteristic properties which do not depend upon the nature of the solute but depend only on the number of particles (molecules or ions) of the solute i.e., on the molar concentration of the solute. These are called colligative properties (colligative, from Latin: co means together, ligare means to bind). Thus, the properties of the solutions which depend only on the number of solute particles but not on the nature of the solute are called colligative properties.

The four important colligative properties are:

1. Relative lowering in vapour pressure
2. Elevation in boiling point
3. Depression in freezing point
4. Osmotic pressure

What is a necessary condition for osmosis to take place?

Semi-permeable membrane

The answer is 1. Semi-permeable membrane.

Osmosis is the movement of water molecules from a region of high water potential to a region of low water potential through a semi-permeable membrane. A semi-permeable membrane is a membrane that allows water molecules to pass through, but not solute molecules.

The other options are not necessary conditions for osmosis to take place. The concentration of the solvent does not affect osmosis, and high temperatures can actually slow down osmosis. Pressure greater than osmotic pressure will cause the water to move from the region of low water potential to the region of high water potential, which is the opposite of osmosis.

Therefore, the only necessary condition for osmosis to take place is a semi-permeable membrane.