What is the composition (mole fraction of benzene) of the first traces of vapour formed? — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The composition of the first trace of vapour is found using Raoult's law: $Y_{\text{benzene}} = \frac{P_{\text{benzene}}^\circ X_{\text{benzene}}}{P_{\text{total}}} = \frac{100 \times 0.5}{70} = \frac{50}{70} \approx 0.714$. Therefore, correct answer is C.