Q1: Physical absorption is

ANS:D - both (b) and (c)

Physical absorption is a reversible phenomenon. Explanation:

1. Physical Absorption:
   • Physical absorption, also known as physisorption, is the process by which molecules of a gas or vapor adhere to the surface of a solid or liquid substance through weak van der Waals forces or other non-covalent interactions.
   • Unlike chemical absorption, which involves chemical reactions between the absorbed molecules and the absorbing substance, physical absorption does not involve chemical changes in the absorbed molecules or the absorbent.
   • Physical absorption is typically a reversible process because the adsorbed molecules can desorb from the surface under suitable conditions, such as changes in temperature or pressure.
   • The adsorption and desorption of molecules during physical absorption are governed by physical forces, such as van der Waals forces, hydrogen bonding, and dipole-dipole interactions.
2. Reversibility:
   • Reversibility implies that the process can be undone, and in the case of physical absorption, the adsorbed molecules can be released from the surface of the absorbent.
   • This reversibility allows physical absorption to be a dynamic process where the concentration of adsorbed molecules can change in response to changes in the external conditions, such as temperature or pressure.
3. Accompanied by Evolution of Heat:
   • Unlike some chemical absorption processes that may be exothermic (release heat) or endothermic (absorb heat), physical absorption generally does not involve a significant evolution or absorption of heat.
   • However, there may be minor temperature changes associated with physical absorption, depending on factors such as the energy of interaction between the adsorbate and adsorbent molecules.
4. Conclusion:
   • Physical absorption is primarily characterized by its reversibility, where adsorbed molecules can be desorbed from the surface of the absorbent, and it may or may not involve significant evolution of heat.