Which of the following is not a characteristic of physical adsorption?

If $x$ amount of gas is adsorbed on $m$ amount of adsorbent at pressure $p$,the Freundlich adsorption isotherm plot gives a straight line for which of the following?

Identify the gas which is readily adsorbed by activated charcoal.

For the adsorption of a gas on a solid,the slope of the linear plot of $\log(x/m)$ versus $\log(p)$ is .... ($n$ is an integer).

To form a complete monolayer of acetic acid on $1 \ g$ of charcoal,$100 \ mL$ of $0.5 \ M$ acetic acid was used. Some of the acetic acid remained unadsorbed. To neutralize the unadsorbed acetic acid,$40 \ mL$ of $1 \ M$ $NaOH$ solution was required. If each molecule of acetic acid occupies $P \times 10^{-23} \ m^2$ surface area on charcoal,the value of $P$ is $\qquad$
[Use given data : Surface area of charcoal $= 1.5 \times 10^2 \ m^2 \ g^{-1}$; Avogadro's number $(N_A) = 6.0 \times 10^{23} \ mol^{-1}$]

Animal charcoal is used in decolourising liquids because it is a good