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

Which one of the following is not a property of physical adsorption?

Identify the gas which is readily adsorbed by activated charcoal.

The graph of $\log(x/m)$ versus $\log p$ is a straight line with an angle of $45^o$ and an intercept of $0.3010$ on the $y$-axis. Calculate the amount of gas adsorbed per gram at a pressure of $0.2 \, atm$.

In Langmuir's model of adsorption of a gas on a solid surface:

$10 \ g$ 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?