Pure benzene freezes t `5.3^(@)C`. A solution of 0.223 g of phenylacetic acid `(C_(6)H_(5)CH_(2)COOH)` in 4.4 g of benzene ` (K_(f) = 5.12 Kkg mol^(-1))` freezes at `4.47^(@)C`. From the observation one can conclude that :

Options

A. phenylacetic acid exists as such in benzene
B. phenylacetic acid undergoes partial ionization in benzene
C. phenylacetic acid undergoes complete ionization in benzene
D. phenylacetic acid dimerizes in benzene

Answer

D

Explanation

Observed molecular mass of phenylacetic acid
`=(1000xx5.12xx0.223)/((5.3-4.47)xx4.4)=312.6`
Calculated molecular mass of `C_(6)H_(5)CH_(2)COOH`
`=72+5+12+2+12+32+1=136`
As observed molecular mass is nearly double of the theoretical value, it dimerizes in benzene.