Answer:- \begin{align*} \text{Given:} & \\ & \text{Mass percentage of toluene} = 30\% \text{ W/W} \\ & \text{Vapour pressure of liquid toluene} (\text{P}_1^0) = 36.7 \text{ mm Hg} \\ & \text{Vapour pressure of liquid benzene} (\text{P}_2^0) = 118.2 \text{ mm Hg} \\ \text{To find:} & \\ 1. & \text{Partial pressures of each constituent} \\ 2. & \text{Total pressure} \\ \text{Formulae:} & \\ 1. & \text{P}_1 = \text{P}_1^0 \cdot x_1 \quad \text{and} \quad \text{P}_2 = \text{P}_2^0 \cdot x_2 \\ 2. & \text{P} = \text{P}_1 + \text{P}_2 \\ \text{Calculation:} & \\ & \text{Molar mass of toluene, C}_7\text{H}_8 = (7 \cdot 12) + (8 \cdot 1) = 92 \text{ g mol}^{-1} \\ & \text{Molar mass of benzene, C}_6\text{H}_6 = (6 \cdot 12) + (6 \cdot 1) = 78 \text{ g mol}^{-1} \\ & \text{Now, 30\% W/W toluene means 30 g toluene in 100 g solution.} \\ & \text{Thus, mass of benzene} = 100 – 30 = 70 \text{ g} \\ & \text{Number of moles of toluene, C}_7\text{H}_8 = \frac{30 \text{ g}}{92 \text{ mol}} = 0.326 \text{ mol} \\ & \text{Number of moles of benzene, C}_6\text{H}_6 = \frac{70 \text{ g}}{78 \text{ mol}} = 0.897 \text{ mol} \\ & \text{Total number of moles} (n_A + n_B) = 0.326 \text{ mol} + 0.897 \text{ mol} = 1.223 \text{ mol} \\ & \text{Mole fraction of toluene (x}_{C_7\text{H}_8}) = \frac{n_A}{n_A + n_B} = \frac{0.326}{1.223} = 0.2666 \\ & \text{Mole fraction of benzene (x}_{C_6\text{H}_6}) = 1.0 – 0.2666 = 0.7334 \\ & \text{Now, using formula (i),} \\ & \text{P}_{C_7\text{H}_8} = \text{P}_{C_7\text{H}_8}^0 \cdot x_{C_7\text{H}_8} = 36.7 \text{ mm Hg} \cdot 0.2666 = 9.78 \text{ mm Hg} \\ & \text{P}_{C_6\text{H}_6} = \text{P}_{C_6\text{H}_6}^0 \cdot x_{C_6\text{H}_6} = 118.2 \text{ mm Hg} \cdot 0.7334 = 86.7 \text{ mm Hg} \\ & \text{Now, using formula (ii),} \\ & \text{Vapour pressure of the solution,} \\ & \text{P} = \text{P}_{C_7\text{H}_8} + \text{P}_{C_6\text{H}_6} = 9.78 \text{ mm Hg} + 86.7 \text{ mm Hg} = 96.48 \text{ mm Hg} = 96.5 \text{ mm Hg} \\ & \therefore \text{Partial pressures of toluene and benzene are 9.78 mm Hg and 86.7 mm Hg, respectively.} \\ & \therefore \text{Total pressure above the solution is 96.5 mm Hg.} \end{align*}