Hydrogen can be separated from natural gas by diffusion through a round tube

rate of separation is given by$,$

N$=2$nDpR

Where,

N$=$ the rate of transport of H$2$ from the tube, gmoles$/($sec$)($cm of length of the tube$)$ D$=$ diffusion coefficient

p$=$ molar density of H$2,$ gmoles$/$cm

R$=$ log mean radius of the tube, $($r $-$ ri$)/$ In$(),$ with r in cm$.$

What are the units of D$?$

$(15$