The vapour pressure of the solution M is — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Following the prompt's instruction to treat the solute (water) as non-volatile, the vapour pressure depends only on the solvent (ethanol). $P = P_{\text{ethanol}}^\circ \times X_{\text{ethanol}} = 40 \times 0.9 = 36.0 \text{ mm Hg}$. Therefore, correct answer is B.