Q1: When adsorption hysteresis is observed, the desorption equilibrium pressure is __________ that obtained by adsorption.

ANS:A - always lower than

"Obtained by adsorption" refers to the equilibrium pressure at which a substance is adsorbed onto a surface. In adsorption, molecules of a gas or liquid adhere to the surface of a solid material, forming a thin film or layer. This process occurs until an equilibrium is reached, where the rate of adsorption equals the rate of desorption, resulting in a stable concentration of molecules on the surface. When discussing the equilibrium pressure obtained by adsorption, it means the pressure of the gas or vapor at which the adsorbate molecules have reached equilibrium with the surface of the adsorbent material. This equilibrium pressure depends on factors such as the nature of the adsorbate and adsorbent, temperature, and the specific conditions of the system. In the context of adsorption hysteresis, which refers to the phenomenon where the desorption curve (plot of desorption equilibrium pressure versus adsorption equilibrium pressure) does not follow the same path as the adsorption curve, the equilibrium pressure obtained by adsorption typically exceeds the equilibrium pressure obtained by desorption. This means that the desorption equilibrium pressure is lower than the adsorption equilibrium pressure, leading to the observed hysteresis loop.