Question

The correct order of adsorption of the following gases on the surface of charcoal is

• A. \(III \gt II \gt I\)
• B. \(III \gt I \gt II\)
• C. \(II \gt I \gt III\)
• D. \(II \gt III \gt I\)

Hint:

The adsorption of gases on solids generally increases with increasing critical temperature and ease of liquefaction: \[ \text{More easily liquefied gas} \Rightarrow \text{Greater adsorption} \] Typical order: \[ SO_2 \gt NH_3 \gt CO_2 \gt CH_4 \gt H_2 \]

Answer 1

The Correct Option is A

A fast way to rank these three gases is to think about how sticky each one is on a surface, and that stickiness tracks closely with how easily a gas turns into a liquid.

Hydrogen is a tiny, non-polar molecule that needs extremely low temperatures to liquefy, so it barely clings to the charcoal surface at all, it should sit at the bottom of the list.

Methane is heavier than hydrogen and liquefies at a noticeably higher temperature, so it is adsorbed more strongly than hydrogen but still fairly weakly.

Sulphur dioxide is a polar molecule with a much higher critical temperature, meaning it condenses most readily of the three, and gases that condense easily also stick to solid surfaces most strongly.

So the strength of adsorption runs SO2 greater than CH4 greater than H2, which in the question's labelling, I equals H2, II equals CH4, III equals SO2, reads as III greater than II greater than I.

So the correct choice is option (1).