Why is the adsorption of a gas on a solid exothermic?

Which of the following forces is responsible for physisorption?

$10 \ g$ of a gas is adsorbed on $500 \ g$ of solid at $10 \ bar$. If the pressure is increased to $20 \ bar$, $14 \ g$ of the gas is adsorbed by the same solid at the same temperature. What is the slope of Freundlich adsorption isotherm?

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 $(N_A) = 6.0 \times 10^{23} \ mol^{-1}$]

What should be taken on the $Y$-axis in the Freundlich adsorption isotherm plot to obtain a straight line?

Assertion : In chemisorption,adsorption first increases with temperature and then decreases.
Reason : Heat keeps on providing more and more activation energy.