Question

Identify the correct statements from the following
I. Adsorption is an endothermic process.
II. Adsorption of a gas on the surface of a solid is accompanied by a decrease in enthalpy and a decrease in entropy.
III. Adsorption capacity of A, B and C gases on 1g of activated charcoal follows the order A>B>C. Their critical temperatures (T$_c$) follow the order T$_c$(A)>T$_c$(B)>T$_c$(C).

• A. I, II only
• B. I, III only
• C. II, III only
• D. I, II, III

Hint:

Adsorption is exothermic, reduces entropy. Higher T$_c$ means stronger van der Waals forces, increasing adsorption. Check thermodynamic signs. Correlate T$_c$ with adsorbability.

Answer 1

The Correct Option is C

1. I: Adsorption is generally exothermic (negative $\Delta H$), as molecules bind to surfaces, releasing energy, so I is incorrect.
2. II: Gas adsorption reduces enthalpy (exothermic) and entropy (molecules lose freedom), correct.
3. III: Higher critical temperature (T$_c$) indicates stronger intermolecular forces, leading to higher adsorption capacity, so A>B>C is correct.
4. Thus, II and III are correct, so the answer is (3) II, III only.