Consider a hemispherical droplet of water residing on a flat surface. The water drop is fully Saturated with air, implying that the flux of air in the our direction is zero the system is at constant team and total pressure P and the diffusivity Dab of water in air and the water vapor pressure P are known under conditions where there is no forced flow of air around the drop determine an expression for the time it takes for the initial radius of the drop R to decrease to R$/2.$ Take water as species and air as species B and assume quasi steady state conditions