Equimolal solutions of KCl and compound X in water shows depressions in freezing point in the ratio of 4:1. Assuming KCl to be completely ionised, the compound X in solution must

Options

A. dissociate to the extent of 50%
B. hydrolyse to the extent of 80%
C. dimerise to the extent of 50%
D. trimerise to the extent of 75%

Answer

D

Explanation

`(DeltaT_f (KCI))/(DeltaT_f (X))=4/1=(i(KCI))/(i(X)) = 2/(i(X)) implies i(X)=0.5`
For association of 3 molecules, `i(X)=1-(1-1/n)alpha=1-(1-1/3)alpha= 0.5 implies alpha = 0.75`