The elevation of boiling point and depression of freezing point of a certain solution of a monobasic acid HA in benzene are ΔTb and ΔTf, respectively. HA exists usually as a monomer, but it dissociates into ions (with degree of dissociation α) at the boiling point Tb of the solution, whereas at the freezing point Tf of the solution, HA exists as (HA)n with a fixed value of n. The molal boiling point elevation constant and molal freezing point depression constants are Kb and Kf respectively. The correct expression for 'n' is:
(1) n= [ΔTb Kb (1+α)] / (ΔTf Kf)
(2) n= (ΔTb Kb) / [ΔTf Kf (1+α)]
(3) n= [ΔTb Kf (1+α)] / (ΔTf Kb)
(4) n= (ΔTb Kf) / [ΔTf Kb (1+α)]
[Ans:(4)]
