Adsorption is always

What do you understand by activation of adsorbent? How is it achieved?

Why is it important to have a clean surface in surface studies?

Which one of the following graphs represents the Freundlich adsorption isotherm?

The plot that best represents the relationship between the extent of adsorption $(x / m)$ and pressure $(p)$ is

The correct option$(s)$ related to adsorption processes is(are):
$A$. Chemisorption results in a unimolecular layer.
$B$. The enthalpy change during physisorption is in the range of $100$ to $140 \ kJ \ mol^{-1}$.
$C$. Chemisorption is an endothermic process.
$D$. Lowering the temperature favors physisorption processes.