Suppose A and B form an ideal solution under a piston. The vapor pressure of pure A is 300 mmHg and that of pure B is 800 mmHg (at the same temperature). If the piston maintains 700 mmHg, what fraction of vapor is present in a 40 mole% A and 60 mole% B mixture. The answer is "there is no vapor present," but I'm having trouble understanding why. Wouldn't the B substance boil, and thus be released as vapor?