Calculate the weight of non-volatile solute having molecular weight $40$,which is dissolved in $57 \ g$ octane to reduce its vapour pressure by $20\%$.

How many grams of solute (molecular weight $60$) are required to be dissolved in $180 \ g$ of water to reduce the vapour pressure to $\frac{5}{6}$ of the pure water?

At $298 \ K$,vapour pressures of two pure liquids $A$ and $B$ are $200 \ mm \ Hg$ and $400 \ mm \ Hg$ respectively. If mole fractions of $A$ and $B$ in solution are $0.7$ and $0.3$ respectively,what is the mole fraction of $B$ in vapour phase?

Calculate the relative lowering of vapour pressure of a solution containing $3 \ g$ urea in $50 \ g$ water. [ Molar mass of urea $= 60 \ g \ mol^{-1} ]$

Which one of the following solutions has the maximum vapour pressure at $27\,^{\circ}C$ temperature?

The vapour pressure of a pure solvent is $0.70 \ atm.$ When a non-volatile solute $A$ is dissolved in it,the vapour pressure of the solution becomes $0.35 \ atm.$ The mole fraction of solute $A$ will be$:-$