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# The vapour pressure of pure water at 37$^{\large\circ}$C is 47.1 torr. What is the vapour pressure of an aqueous solution at 37$^{\large\circ}$C containing 20 g of glucose dissolved in 500 gm of water?

$n_{H_2O}=\large\frac{500}{18}$$=27.78mol n_{glucose}=\large\frac{20}{180}=$$0.11mol$
$X_{H_2O}=\large\frac{n_{H_2O}}{n_{H_2O}+n_{glucose}}$
$\Rightarrow 0.996$
According to Raoult’s law,
$P_{H_2O}=P_{H_2O}^0X_{H_2O}=47.1\times 0.996=46.9$torr
Hence (A) is the correct answer.