Question Stem (Q15 & Q16): Two volatile liquids A and B form an ideal solution. Consider a 5 molal solution of B in A inside a closed container having a total vapour pressure of 100 mm Hg at 300 K. The vapour pressure of pure A at 300 K is 105 mm Hg. Assume that A and B behave as ideal gases in the vapour phase.

Given: The gas constant $$R=0.08$$ L atm K$$^{-1}$$ mol$$^{-1}$$;
Molar mass of A is 50 g mol$$^{-1}$$;
Molar mass of B is 57 g mol$$^{-1}$$;
Density of liquid B at 300 K is 0.5 g/mL; 1 atm $$=760$$ mm Hg.

The mole fraction of B in vapour phase which is in equilibrium with this solution is ___.