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A solution `M` is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is `0.9` Given: Freezing point depression constant of water `(K_(f)^(water)=1.86 K kg mol^(-1))` Freezing point depression constant to ethanol `(K_(f)^(ethanol))=2.0 K kg mol^(-1))` Boiling point elevation constant of water `(K_(b)^(water))=0.52 K kg mol^(-1))` Boiling point elevation constant of ethanol `(K_(b)^(ethanol))=1.2 K kg mol^(-1))` Standard freezing point of water = `273 K ` Standard freezing point of ethanol = `155.7 K ` Standard boiling point of water = `373 K ` Standard boiling point of ethanol = `351.5 K ` Vapour pressure of pure water =`32.8 mm Hg` Vapour pressure of pure ethanol =`40 mm Hg` Molecular weight of water =`18 g mol^(-1)` Molecular weight of ethanol =`46 g mol^(-1)` In anwering the following questions consider the solutions to be ideal dilute solutions and solutes to be non-volatile and non-dissociative. The vapour pressure of the solution `M` isA. `39.3 mm Hg`B. `36.0 mm Hg`C. `29.5 mm Hg`D. `28.8 mm Hg`

Answer» Correct Answer - B
`P_("Total")=P_(A)^(@) = P_(A)^(@)chi_(A) [:.` Solute is to be taken as non-volatile]
`=40 xx 0.9 =36 mm Hg`


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