The freezing point of 0.02mole fraction solution of acetic acid in benzene is 277.4K.Assuming molality equal to molarity,calculate $K_c$ for the equilibrium reaction $2CH_3COOH \;\;\leftrightharpoons\;\;(CH_3COOH)_2$.

Question

$\begin{array}{1 1}2.787M^{-1}\\3.787M^{-1}\\4.787M^{-1}\\5.787M^{-1}\end{array}$