The amount of gas adsorbed (x/m) is the function of temperatureand pressure, which can be shown as under (x)/(m)= f(p,T) The variation x/m and p, at constant temperature is known as adsorption isotherm i.e., x/m=f(p) at constant temperature Seven type of physisorption isotherms are known. Some of them are shown below Physisorption Type I. Where there is formation of monolayer on the surface of adsorbent, this typeof curve is obtained. Physisorption Type II. The transition point 'X' of this physisorption isotherm indicates, that the formation of mono layer is complete and that of multilayer is started. Physisorption Type III. This isotherm has no transition point. In this type of curve, the multimolecular starts before the completion of monomolecular layer. On the basis of this comprehension, answer teh following question from the physisorption isotherm of a gas on a solid shown as under. The portion ''OX'' of the physisorption isotherm represents