Pure benzene freezes at 5.3oC. A solution of 0.223 g of phenylacetic acid C6H2CH2COOHin 4.4 g of benzene Kf=5.12 K kg mol-1freezes at 4.47oC.From this observation, one can conclude that

Depression in freezing point, ΔTf=Kfm                                (where, m = molality)=5.12×0.223×10004.4×136[∵ mol. w.t. of phenylacetic acid =136]=5.12×0.372=1.91∘C∴Theoretical ΔTf=1.91 Actual ΔTf=5.3∘C−4.47∘C=0.83∘C∴           i=0.831.91=0.43 ∵                  i<1∴Association will take Place.Th1s, it can be said that phenylacetic acid dimerises in benzene.