But the sum of the mole fractions of the components of a solution must equal 1; that is (xA+ XE SO (R=I-x. Therefore Ap=pa 0·xB From this equation, we can see that the vapor-pressure lowering is a colligative property--one that depends on the concentration but not on the nature of the solutionBut the sum of the mole fractions of the components of a solution must equal 1 ; that is ( xA + xB = 1 ). So (xB = 1 – xA). Therefore, p = pA 0 · xB From this equation,we can see that the vapor-pressure lowering is a colligative property—one that depends on the concentration, but not on the nature, of the solution