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.
Osmotic pressure (Π) of a solution does not depend upon
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Nature of solute particles.
Osmotic pressure is a colligative property: it depends on the number of solute particles in a given volume of solution and not on what those particles are. For a dilute solution:
\( \displaystyle \pi = C\,R\,T = \frac{n_2}{V}\,R\,T \)
The formula contains the amount of solute (n2), the volume and the temperature, but nothing that describes the chemical nature of the solute. A 0.1 M solution of glucose and a 0.1 M solution of urea have the same osmotic pressure at the same temperature.
Option (1) Number of solute molecules. — A factor that osmotic pressure depends on. Osmotic pressure is proportional to n2; this is why a dissociating solute, which gives more particles, shows a higher value.
Option (2) Temperature. — A factor that osmotic pressure depends on. π is proportional to the absolute temperature T.
Option (3) Concentration of solution. — A factor that osmotic pressure depends on. π is proportional to the molar concentration C.
Option (4) Nature of solute particles. — Not a factor that osmotic pressure depends on. As a colligative property it depends only on the number of particles: 0.1 M glucose and 0.1 M urea have the same osmotic pressure at the same temperature.
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – …
