Explain the types of adsorption.

(N/A) There are mainly two types of adsorption of gases on solids:
$1$. $\text{Physical adsorption (Physisorption)}$: If the accumulation of gas on the surface of a solid occurs due to weak van der Waals' forces,it is termed as physical adsorption.
$2$. $\text{Chemical adsorption (Chemisorption)}$: When the gas molecules or atoms are held to the solid surface by chemical bonds (covalent or ionic),the adsorption is termed as chemical adsorption. It involves a high energy of activation and is often referred to as activated adsorption.
Sometimes,these two processes occur simultaneously. $A$ physical adsorption at low temperature may pass into chemisorption as the temperature is increased. For example,$H_2$ is first adsorbed on $Ni$ by van der Waals' forces,and then the molecules dissociate to form hydrogen atoms held by chemisorption.