Colligative properties are applicable to:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → dilute solution
Colligative properties (relative lowering of vapour pressure, elevation of boiling point, depression of freezing point and osmotic pressure) depend only on the number of solute particles, not on their nature. Their formulas rest on Raoult’s law, which holds when the solution behaves as an ideal solution. That is true only for dilute solutions, where solute particles are far apart and do not interact with each other. For example:
\( \displaystyle \Delta T_b = K_b\,m \qquad \Delta T_f = K_f\,m \qquad \pi = CRT \)
In a concentrated solution, solute–solute and solute–solvent interactions make the solution deviate from Raoult’s law, and these simple relations no longer hold. So colligative properties apply to dilute solutions.
Why the other options are incorrect
Option (2) solid solutions — Incorrect. The colligative relations are derived for a non-volatile solute in a liquid solvent; boiling point elevation and osmotic pressure have no meaning for an alloy.
Option (3) concentrated solutions — Incorrect. These deviate from ideal behaviour, so the measured values do not follow \( \Delta T_b = K_b m \) and similar relations.
Option (4) only aqueous solution — Incorrect. The solvent can be anything; benzene, for example, has its own \( K_b \) and \( K_f \).