Hydrogen can be adsorbed in the interstitial spaces between $Pd$ atoms. This phenomenon is known as ...........

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: In expensive scientific instruments,silica gel is kept in watch-glasses or in semipermeable membrane bags.
Reason $(R)$: Silica gel adsorbs moisture from air via adsorption,thus protects the instrument from water corrosion (rusting) and/or prevents malfunctioning.
In the light of the above statements,choose the correct answer from the options given below:

Why is adsorption always exothermic?

Given the following data:

Gas	$H_2$	$CH_4$	$CO_2$	$SO_2$
Critical Temp $/ K$	$33$	$190$	$304$	$630$

Based on the data provided,predict which of the following gases shows the least adsorption on a definite amount of charcoal.

Freundlich adsorption isotherm gives a straight line on plotting :-

Amongst the following statements regarding adsorption,those that are valid are :
$(a)$ $\Delta H$ becomes less negative as adsorption proceeds.
$(b)$ On a given adsorbent,ammonia is adsorbed more than nitrogen gas.
$(c)$ On adsorption,the residual force acting along the surface of the adsorbent increases.
$(d)$ With increase in temperature,the equilibrium concentration of adsorbate increases.