$3.$ Component A diffuses through a stagnant gas film which has a thickness of $5$ cm in a flatcatalyst surface to the surface of the catalyst and it undergoes the instantaneous reactionA$($g$)->3$B$($g$).$ Gas B then diffuses from the catalyst surface. The concentration of componentA is $0\mathrm{.}7$ mol$/$cm$3$ within the gas film. Assuming the steady state conditions;a$)$ Derive the concentration profile of the system.b$)$ Find the molar flux.