Which statement best describes colligative properties?

• A. They depend on the identity of dissolved particles.
• B. Boiling-point elevation and freezing-point depression depend on the number of dissolved particles.
• C. They are independent of temperature.
• D. They affect only the color of solutions.

Answer: (B)

Colligative properties depend on how many dissolved particles are present, not on what those particles are. Boiling-point elevation and freezing-point depression rise with the number of particles in solution because each particle disrupts the solvent’s normal behavior—raising the energy needed to boil and lowering the energy at which the solvent solidifies. This relationship is captured by expressions like ΔTb = i Kb m and ΔTf = i Kf m, where i is the van’t Hoff factor (how many particles a solute produces) and m is the molality. So, for the same amount of solute, a substance that dissociates into more particles (higher i) will produce a larger effect than one that doesn’t dissociate. That’s why the statement about boiling-point elevation and freezing-point depression depending on the number of dissolved particles is the best description. The other ideas—dependence on particle identity, independence from temperature, or affecting color—don’t describe colligative properties.