Chemistry · Solutions and Colligative Properties

Two liquids 'A' and 'B' form an ideal solution. At 300 K, the vapour pressure of a solution containing 1 mole of 'A' and 3 moles of 'B' is 550 mm Hg. At the same temperature, if one more mole of 'B' is added to the solution, the vapour pressure of the solution increases to 560 mm Hg. The ratio of the vapour pressures of A and B in their pure state (pA° : pB°) is: