A substance ' X ' 
dissolved in 150 g of a solvent ' Y ' (molar mass 
) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent ' Y ' is 
. (nearest integer)
[Given : 
of the solvent 
]
Assume the solution to be dilute and no association or dissociation of 
takes place in solution.
Text Solution
Verified by Experts3
(3)
Using boiling point elevation to find molality:
gives 
, so 
.
Converting molality to moles of solute:
, giving moles of 
.
Molar mass of 
.
For vapor pressure lowering, the relative lowering equals the mole fraction of solute.
Moles of solvent 
.
Relative lowering of vapor pressure
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