Benzoic acid molecules undergo dimerisation in benzene. 2.44 g of benzoic acid when dissolved in 30 g of benzene caused depression in freezing point of 2 K . What is the percentage of association of it?

(Given $K_f\left(\mathrm{C}_6 \mathrm{H}_6\right)=5 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$; molar mass of benzoic acid $=122 \mathrm{~g} \mathrm{~mol}^{-1}$ )

At $T(\mathrm{~K})$, the vapour pressure of pure benzene and toluene are 75 and 22 mm Hg respectively. 23.4 g of benzene and 64.4 g of toluene are mixed to form an ideal solution. If the vapours are in equilibrium with the liquid mixture, the mole fraction of toluene in vapour phase (At.wt. of $\mathrm{C}=12, \mathrm{H}=1$ )

1.95 g of non-volatile and non-electrolyte solute dissolved in 100 g of benzene lowered the freezing point of it by 0.64 K .

The molar mass of the solute (in $\mathrm{g} \mathrm{mol}^{-1}$ )

$$ \left(K_f\left(\mathrm{C}_6 \mathrm{H}_6\right)=5.12 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right) $$