4. Consider a desiccant in contact with humid air. At equilibrium, the vapor pressure PH2 of H2O in the air will reach a constant value, as will the H2O saturation fraction of the desiccant. A) Find PH2O in terms of f and the "reference" chemical potential for H2O in air, assuming humid air is ideal. B) Let's say you find that, when left out in the ambient environment (relative humidity of 50% ), desiccant will reach an equilibrium H2O saturation of 10%. What is the maximum saturation that a desiccant can have, if it is to keep the relative humidity of surrounding air below 5%