Osmotic pressure is the pressure that stops the flow of a solvent and is related to the volume as:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Inversely proportional to the volume.
For dilute solutions, osmotic pressure is proportional to the molarity of the solution, and molarity is moles of solute per litre of solution:
\( \displaystyle \pi = CRT = \frac{n_2}{V}RT \)
For a given amount of solute (n2) at a given temperature, \( \displaystyle \pi \propto \frac{1}{V} \): doubling the volume halves the osmotic pressure. So osmotic pressure is inversely proportional to the volume, like the pressure of a gas in Boyle’s law.
Why the other options are incorrect
Option (1) Directly proportional to the volume. — Incorrect. Diluting a solution to a larger volume lowers its concentration and so lowers π; it does not raise it.
Option (3) Equal to the volume. — Incorrect. Pressure and volume have different units and cannot be equal.
Option (4) More than the volume of the solvent. — Incorrect. A pressure cannot be compared with a volume; the relation is \( \pi V = n_2RT \).
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – “… The osmotic pressure of a solution is the excess pressure that must be applied to a solution to prevent osmosis, i.e., to stop the passage of solvent molecules through a semipermeable membrane into the solution. This is illustrated in Fig. 1.10. Osmotic pressure is a colligative property as it depends on the number of solute molecules and not on their identity. For dilute solutions, it has been found experimentally that osmotic pressure is proportional to the molarity, C of the solution at a given temperature T. Thus:
Π = C R T (1.39)
Here Π is the osmotic pressure and R is the gas constant.
Π = (n2 /V) R T (1.40)
Here V is volume of a solution in litres containing n2 moles of solute.”