Benzene and toluene form an ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at \(T(\mathrm{~K})\) are \(50 \mathrm{~mm} \mathrm{Hg}\) and \(40 \mathrm{~mm} \mathrm{Hg}\) respectively. What is the mole fraction of toluene in vapour phase when \(117 \mathrm{~g}\) of benzene is mixed with \(46 \mathrm{~g}\) of toluene? (molar mass of benzene and toluene are 78 and \(92 \mathrm{~g} \mathrm{~mol}^{-1}\) respectively)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.