The mean$-$free path between collisions of gas molecules depends on pressure. At what

pressure will the mean$-$free path of spherical molecules $(0\mathrm{.}3-nm$ in diameter$)$ be equal to

$20nm?$ Note that this is the pressure at which bulk diffusion and Knudsen diffusion are

equally important when the diameter of catalyst pores is $20nm.$ Perform the calculation

at $500K.$ Make other reasonable assumptions that you deem necessary $($e$.$g$.,$ Molecular

weight is $30\frac{g}{m}ol,$ etc.$).$