Which of the following statements regarding osmosis is not correct?

The correct answer is Option (4) → It is common in liquids as well as in gases.

Osmosis is the flow of solvent molecules through a semipermeable membrane from the pure solvent (or a dilute solution) into a more concentrated solution. The membrane lets the solvent through but holds back the solute particles. It is a property of solutions, so it is a liquid-phase process; gases mix freely by diffusion and do not show osmosis.

• Option (1) The direction of osmosis can be reversed if a pressure larger than the osmotic pressure is applied to the solution side. — A correct statement about osmosis. This is reverse osmosis: the pure solvent is then squeezed out of the solution through the membrane.

• Option (2) Reverse osmosis is used in the desalination of sea water. — A correct statement about osmosis. Pure water is forced out of sea water through a membrane such as cellulose acetate, which holds back the salts.

• Option (3) It involves the movement of solvent across semi-permeable membranes only. — A correct statement about osmosis. Only the solvent passes; solute particles cannot cross the semipermeable membrane.

• Option (4) It is common in liquids as well as in gases. — Not a correct statement about osmosis. Osmosis is a flow of solvent through a semipermeable membrane between solutions; gases do not show it.

NCERT (2026-27 edition):
Reverse Osmosis and Water Purification

Osmosis and Osmotic Pressure – “… Assume that only solvent molecules can pass through these semi-permeable membranes. If this membrane is placed between the solvent and solution … the solvent molecules will flow through the membrane from pure solvent to the solution. This process of flow of the solvent is called osmosis.”