$20-$ Benzene is stored in a tank of $1m$ diameter and open at atmosphere at the top. A stagnant air film $0\mathrm{.}1m$ thick is covering the benzene surface above which there is no benzene. If the atmospheric temperature is $298K$ and the corresponding vapor pressure of benzene is $20000Pa,$ estimate the rate of loss of benzene in $mo\frac{l}{h}.$ Diffusivity of benzene is $0\mathrm{.}02\frac{m^2}{h},$ total pressure is $101325Pa,R=8\mathrm{.}314\frac{m^3*Pa}{\text{m}\text{o}\text{l}\text{.}K}.$