Liquid A and B form an ideal solution. The vapour pressure of pure liquids A and B are \( 350 \) and \( 750 \) mm Hg respectively at the same temperature. If \( X_A \) and \( X_B \) are the mole fraction of A and B in solution while \( Y_A \) and \( Y_B \) are the mole fraction of A and B in vapour phase then,