A) solute molecules to the solvent molecules
B) solute molecules to the total molecules the solution
C) solvent molecules to the total molecules B in the solution
D) solvent molecules to the total number ions of the solute
Correct Answer: B
Solution :
According to Raoulfs law, relative lowering in vapour pressure is directly proportional to the mole fraction of solute, ie, \[\frac{{{P}^{o}}-P}{{{P}^{o}}}{{\chi }_{s}}\] where \[{{\chi }_{s}}=\frac{{{n}_{s}}}{{{n}_{s}}+N}=\frac{moles\,of\,solute}{total\,number\,of\,moles}\] \[\therefore \]relative lowering of vapour pressure \[=\frac{{{n}_{2}}}{{{n}_{1}}+{{n}_{2}}}=\frac{solute\,molecules}{total\,molecules\,in\,the\,solution}\]
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