The answer is (A) Ionic solutes dissociate in solution causing an enhancement of all colligative properties.
Explanation:
When a solute dissociates in solution, it causes changes in colligative properties. In several properties an increase is produced (like in boiling point) whereas in others a decrease is produced (like in melting point and vapor pressure). Colligative properties are these that depend of the number of solute particles there are in a solution. Raoult's law is about vapor pressure of a solvent, and it says that the vapor pressure of a solvent decreases when a solute is added. As greater the number of solute particles in solution, lesser the vapor pressure of the solvent. That is due to the fact that solute particles interact with solvent molecules and avoid its escape to gas phase. So, there are less solute particles in gas phase and consequently its vapor pressure is less.
