Which of the following is not a characteristic of chemisorption?

In Freundlich adsorption,the amount of gas adsorbed is proportional to pressure $P$ as

$50 \ mL$ of $1 \ M$ oxalic acid is shaken with $0.5 \ g$ of wood charcoal. The final concentration of the solution after adsorption is $0.5 \ M$. The amount of oxalic acid adsorbed per $g$ of charcoal is ....... $g$.

The Freundlich adsorption isotherm is given by:

Adsorption is multilayer in case of

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: