Pure benzece freezes at 5.45oC at a certain place but a 0.374 m solution of tetrachlororthane in benzene freezes at 3.55oC .The Kf for benzene is-
given,
Tinitial=5.45OC
Tfinal=3.55OC
molality - 0.374 m
Depression of freezing point ΔT=Tfinal−Tinitial
= |3.55−5.45|=1.9
ΔT=mKf
Kf - freezing point constant
Kf=ΔTm
Kf=1.90.374=5.08 KKgmol−1
Hence, option(a) is the correct answer.