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