Adsorption

Adsorption is a process of deposition of molecules on the surface of another substance. It occurs in two ways:

• Physisorption
• Chemisorption

Physical adsorption is a reversible process. It occurs due to the non-covalent attraction between adsorbate and adsorbent. In Physisorption, the two molecules are held together by weak intermolecular forces i.e. van der Waal forces, hence it is reversible. With increase in temperature, physical adsorption of substances decreases. Since in physisorption, molecules are held together by weak forces of attraction, therefore its energy of adsorption is also low as compared to chemisorption. Hence, only the fourth statement is incorrect here. 

In Chemisorption, the adsorbate and adsorbent are held together by strong covalent bonds, therefore this process is irreversible and requires high adsorption energy.