Properties of a solution that depend only on the number of solute molecules, and not the identity of the solute?

• A. Boiling Point Elevation
• B. Mass percent
• C. Colligative properties
• D. Mole fraction

Answer: (C)

Colligative properties describe how a solution changes because of the number of dissolved particles, not what those particles are. The effect depends on how many solute particles are present (and, if the solute dissociates, on the effective number of particles via the van’t Hoff factor), so changing the solute to a different substance while keeping the particle count the same produces the same change in properties like boiling point, freezing point, vapor pressure, and osmotic pressure. Boiling point elevation is one example of this behavior, but the general term that covers all such effects is colligative properties. Mass percent and mole fraction are about composition, not about how those particles alter the solvent’s physical properties, so they’re not the describing concept here.