What is the composition (mole fraction of benzene) of the last trace of liquid? — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The composition of the last trace of liquid is in equilibrium with the dew point vapour. $X_{\text{benzene}} = \frac{Y_{\text{benzene}} P}{P_{\text{benzene}}^\circ} = \frac{0.5 \times (400/7)}{100} = \frac{200/7}{100} = \frac{2}{7} \approx 0.286$. Therefore, correct answer is D.