The vapour pressure of the solution of two liquids A(pº = 80 mm) and B(pº = 120 mm) is found to be 100 mm when xA = 0.4. The result shows thatAnswers(a)solution exhibits ideal behaviour(b)solution shows positive deviations(c)solution shows negative deviations(d)solution will show positive deviations for lower concentration and negative deviations for higher concentrations.

Pressure of solutionP=X_A*P_A....+...X_B*P_B
where X=mole fraction of components and if it holds true for the given data then it is following Rault’s law and so it is called ideal solution. Otherwise the solution is non-ideal in nature either with positive deviation(when the total pressure P is higher than expected) or negative deviation(when the total pressure P islower than expected).
Now please check the equation; you will get it!!