Which of the following forces is responsible for physisorption?

Froth floatation process for concentration of ores is an illustration of the practical application of:

Adsorption is multilayer in case of

Give an explanation of the applications of adsorption.

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.

Arrange the gases $H_2, CH_4, CO_2,$ and $NH_3$ in the order of their volume adsorbed on $1 \ g$ of charcoal at $288 \ K$.