The freezing point of benzene decreases by $0.45^{\circ}C$ when $0.2\; g \%$ of acetic acid is added to $20\; g$ of benzene. If acetic acid associates to form a dimer in benzene,percentage association of acetic acid in benzene will be : $(Kf$ for benzene=$5.12 \;K \;kg mol^{−1})$

Question

$\begin{array}{1 1} (1) 74.6\% \\ (2) 94.6 \% \\ (3) 64.6 \% \\ (4) 80.4 \% \end{array}$