【正确答案】The freezing point depression, Δt, is (5. 5 - 4. 2)℃= 1.3℃
   m=Δt/K=1.3℃/5.12℃/m=0.25m
   The solution contains 100 g of solute/kg of benzene. It contains 0.25 mol solute/kg of benzene, as determined from the freezing point depression. Thus the molecular weight is
   100 g/0.25 mol=400 g/mol