alleryIf a solute dimerises in solution, its observed molar mass compared with the calculated value will be
ATwice the calculated value
BEqual to the calculated value
CHalf the calculated value
DFour times the calculated value
Answer & Solution
Correct answer: A. Twice the calculated value
1. Colligative properties measure the number of solute particles.
2. Dimerisation reduces the number of particles by half (2 molecules → 1 dimer).
3. The measured colligative effect is halved, so the apparent (observed) molar mass appears doubled.
4. Van't Hoff factor i = 0.5 for complete dimerisation.
_Source: syllabus Chemistry, Unit 1 "Solutions", §1.7_
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