Sol. $$ \begin{aligned} & 2=0.52 \times \mathrm{m} \\ & \mathrm{~m}=\frac{2}{0.52} \end{aligned} $$ According to question, solution is much diluted $\begin{aligned} & \text { so } \frac{\Delta \mathrm{P}}{\mathrm{P}^0}=\frac{\mathrm{n}_{\text {solute }}}{\mathrm{n}_{\text {solvent }}} \\ & \frac{\Delta \mathrm{P}}{\mathrm{P}^0}=\frac{\mathrm{m}}{1000} \times \mathrm{M}_{\text {solvent }} \\ & \Delta \mathrm{P}=\mathrm{P}^0 \times \frac{\mathrm{m}}{1000} \times \mathrm{M}_{\text {solvent }} \\ & =760 \times \frac{\frac{2}{0.52}}{1000} \times 18=52.615 \\ & \mathrm{P}_5=760-52.615=707.385 \mathrm{~mm} \text { of } \mathrm{Hg}\end{aligned}$