The properties of solutions which depend on the number of solute particles and are independent of their chemical identity are called colligative properties. These are lowering of vapour pressure, elevation of boiling point, depression of freezing point and osmotic pressure. The process of osmosis can be reversed if a pressure higher than the osmotic pressure is applied to the solution. Colligative properties have been used to determine the molar mass of solutes. Solutes which dissociate in solution exhibit molar mass lower than the actual molar mass and those which associate show higher molar mass than their actual values. Quantitatively, the extent to which a solute is dissociated or associated can be expressed by van’t Hoff factor i. This factor has been defined as ratio of normal molar mass to experimentally determined molar mass or as the ratio of observed colligative property to the calculated colligative property.

Which of the following relation represents correct relationship of osmotic pressure with concentration of the solution?

π ∝ c

The correct answer is 4. \(\pi \propto c\)

Osmotic pressure (\(\pi\)) is a colligative property of a solution, meaning it depends on the number of solute particles in the solution but not on the nature of the solute particles. Osmotic pressure is directly proportional to the concentration of the solute in the solution.
The mathematical expression that describes the relationship between osmotic pressure (\(\pi\)) and concentration (\(c\)) is given by the van't Hoff equation:
\[ \pi = i \cdot M \cdot R \cdot T \]
where:
- \(\pi\) is the osmotic pressure,
- \(i\) is the van't Hoff factor (the number of particles into which the solute dissociates in the solution),
- \(M\) is the molarity of the solution,
- \(R\) is the ideal gas constant,
- \(T\) is the absolute temperature.
For a non-ionic solute that does not dissociate in the solution, \(i\) is equal to 1. In such cases, the equation simplifies to:
\[ \pi = M \cdot R \cdot T \]
This equation clearly shows that osmotic pressure (\(\pi\)) is directly proportional to the molarity (\(M\)) of the solution, as \(R\) and \(T\) are constants and molarity \(M\) depends on the concentration.
Therefore, the correct relationship is:
\[ \pi \propto c \]
This means that as the concentration of the solute in the solution increases, the osmotic pressure will also increase proportionally. The correct option from the provided choices is:
4. \( \pi \propto c \)