Read the passage carefully and answer the questions.
The osmotic pressure is one of the four colligative properties which depends on the number of particles of solute in the solution, irrespective of their nature. The osmotic pressure is equal to the product of concentration, gas constant and temperature. It is the most commonly used property for the determination of the molar mass of biomolecules. In many situations, the molecules get dissociated or associated when they are dissolved in a solvent, thereby changing the number of molecules in the solution. As a result, an abnormal molecular mass is obtained. The extent of dissociation or association is given by van't Hoff factor (i), which is the ratio of normal molar mass to abnormal molar mass. It is related with the degree of association or ionization. The introduction of van't Hoff factor in the osmotic pressure equation modifies the equation.
How is the osmotic pressure of a concentrated solution related to the osmotic pressure of a dilute solution of the same substance at a given temperature?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Higher than that of its dilute solution.
Osmotic pressure is a colligative property: it depends on the number of solute particles per unit volume. For a dilute solution it is given by
\( \pi = CRT \)
where C is the molar concentration. At a given temperature, R and T are fixed, so π is proportional to C. A concentrated solution of the same substance has a larger C, so its osmotic pressure is higher.
Why the other options are incorrect
Option (1) Lower than that of its dilute solution. — Incorrect. This would need π to fall as C rises, the reverse of π = CRT.
Option (2) Same as its dilute solution. — Incorrect. π would be the same only if the concentrations were the same.
Option (4) Cannot compare on concentration basis until we know the nature of that solute. — Incorrect. Both are solutions of the same substance at the same temperature, so the solute is the same in both. π = CRT then compares them directly through their concentrations.
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 29-05 S2 | – | 25-05 S3 | – |