12. The figure shows a region very close to the surface of a solid catalyst where a reaction, A -2B, occurs at the catalyst surface: i.e. at z=0. If the bulk gas contains a 5050 molar mix of ' A ' and ' B ' (XAB=0.05), answer the following questions for steady-state. a. Express NAZ in terms of the concentration gradient of ' A ' b. Using the superimposed grid shown in the figure, sketch the concentration profile for ' A ' if the reaction is instantaneous. c. Repeat (b) if the reaction occurs at a finite rate. d. Repeat (b) if the surface reaction is instantaneous but some reaction also occurs in the gas film and is first order with respect to ' A