Brunauer, Emmet and Teller (BET) equation is used to determine the specific surface area of a porous particle but not the pore volume & the porosity of the catalyst bed. Which of the following postulates is not used to derive BET equation ?

A. Langmuir’s assumption applies to every adsorbed layer
B. There is no dynamic equilibrium between successive layer
C. The adsorbed layer may be polymolecular in thickness and the heat of adsorption in each layer
(except the first one) is involved in each of the evaporation process
D. None of these