A 5% solution of cane sugar is isotonic with 0.5% of X. The molecular weight of substance X is

$$\begin{gathered} {\mathrm{\pi }}_{\mathrm{canesugar}}={\mathrm{\pi }}_{\mathrm{X}} (\because \mathrm{they} \mathrm{are} \mathrm{isotonic}) \\ {\mathrm{C}}_{\mathrm{canesugar}}={\mathrm{C}}_{\mathrm{X}} (\because \mathrm{\pi }=\mathrm{CRT}, \mathrm{C}=\mathrm{Molarity}) \\ \frac{5\times 10}{342}=\frac{0.5\times 10}{{\mathrm{M}}_{\mathrm{X}}} \left(\because \mathrm{Molarity}=\frac{(\mathrm{w}/\mathrm{v})\%\times 10}{\mathrm{Molar} \mathrm{mass}}\right) \\ {\mathrm{M}}_{\mathrm{X}}=\frac{342\times 0.5}{5}=34.2\mathrm{gm} \end{gathered}$$