$($b$)$ How does the relationship n $=$ f$(,)$ compare with Eq$.(11-55)?$ What is the relationship between I, and $?$

$($c$)$ Comparison of the definitions of $$,[$derived in part $($a$)]$ and $[$from Eq$.(11-56)]$ leads to what relationship between the effective diffusivity D$.$ in a flat plate of catalyst and the diffusivity D for a single pore? Note that L$,$ the actual thickness of one$-$half the slab in Eq$.(11-56),$ is one$-$half the pore length. Also note that k$$ in Eq$.(11-56)$ is equal to k$$S$.$

$($d$)$ What simple model of a porous catalyst will explain the relation between De and D$?$ Assume that the Wheeler equation relating the pore radius, the pore volume, and the surface area $[$Eq$.(11-21)]$ is applicable.