Answer: dissociation or association of the solute.
- A an unusually high temperature applied
- B dissociation or association of the solute
- C an unusually high external pressure
- D the presence of an active catalyst
Correct answer: B. dissociation or association of the solute
Explanation: When the solute dissociates or associates, the actual particle count differs from that assumed, giving an abnormal molar mass.
Adding a non-volatile solute lowers the solvent's vapour pressure at every temperature, which is the root cause behind all four colligative properties: it shifts the freezing point down and the boiling point up.
Concept context
Learn how substances dissolve and form mixtures. Covers concentration terms, colligative properties (boiling point elevation, freezing point depression, osmotic pressure), and ideal vs non-ideal solution behaviour.