$20.)$ Nitrogen gas concentration across a $2mm$ thick palladium sheet changes by $4k\frac{g}{m^3}.$

Considering steady$-$state diffusion with diffusion constant ${10}^{-10}\frac{m^2}{s},$ diffusion flux is

$k\frac{g}{m^2}*s$:

a$)2{10}^{10}$

b$)2{10}^{-10}$

c$)5{10}^{-11}$

d$)5{10}^9$