One strategy to lower the concentration of certain substances in gas mixtures is to put the gas in contact with a liquid, since the gases will be absorbed in different amounts depending on the type of gas. Such a process unit in the chemical process industry is called an absorber. 

In an intermediate calculation to size an absorber, you need to determine the partial pressure of benzene in the vapor phase, in equilibrium with a liquid composed of  99.9 mol% water and 0.1 mol% benzene. You know the infinite dilution activity coefficient for benzene in water at this temperature is 2500.