Which of the following gases is readily adsorbed by solid adsorbent?

The volumes of gases $H_2, CH_4, CO_2$ and $NH_3$ adsorbed by $1 \ g$ of charcoal at $288 \ K$ are in the order:

Assertion : The enthalpy of physisorption is greater than chemisorption.
Reason : Molecules of adsorbate and adsorbent are held by van der Waal's forces in physisorption and by chemical bonds in chemisorption.

Adsorption due to strong chemical forces is called

What are the factors which influence the adsorption of a gas on a solid?

Compare the enthalpy of chemical adsorption with physical adsorption.