Question:

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

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Adsorption is exothermic; residual forces on the surface decrease on adsorption; ammonia is easily liquefied so it adsorbs more than N2; at higher temperature adsorption decreases.
Updated On: Nov 5, 2026
  • (c) and (d)
  • (a) and (b)
  • (d) and (a)
  • (b) and (c)
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The Correct Option is B

Solution and Explanation

(a) As adsorption proceeds the surface becomes progressively covered, so the heat of adsorption (\(\Delta H\), negative) becomes less negative. Valid.
(b) Easily liquefiable gases with a higher critical temperature (NH3) are adsorbed more than gases like N2 because of stronger van der Waals forces. Valid.
(c) Adsorption satisfies the unbalanced (residual) forces at the surface, so they decrease, not increase. Not valid.
(d) Adsorption is exothermic, so by Le Chatelier's principle the amount adsorbed at equilibrium decreases with rise in temperature. Not valid.
So the valid statements are (a) and (b).
Answer: (2) (a) and (b)
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