At 20^oC, the vapour pressure of diethyl ether is 442mm. When 6.4g. of a non-volatile solute is dissolved in 50g. of ether, the vapour pressure falls to 410mm. The Molecular weight of the solute is
 

Given, P = 442mm and P' = 410mm

thus $∆P=\mathrm{P}-\mathrm{P}\text{'}=(442-410)\mathrm{mm}=32\mathrm{mm}$

Given mass of solvent = 50g

molar mass of solvent =  74g

using the formula:$∆P/P=W_1{M}_1/W_2{M}_2$

$$\begin{gathered} \frac{32}{442}=\frac{6.4}{50}\times \frac{74 }{m} \\ m=130.8323g \end{gathered}$$

Hence, the correct option (C). 130.8323g