Because adsorption is exothermic process. With increase in temperature extent of adsorption will decrease

Adsorption of a Gas on the Surface of a Solid

Introduction:
Adsorption is the process by which a substance (gas, liquid, or solute) accumulates on the surface of a solid or liquid. In the case of a gas adsorbing on the surface of a solid, there are certain characteristics and behaviors that are observed.

A) On increasing temperature, adsorption increases:
This statement is incorrect. In general, adsorption decreases with an increase in temperature. This is because an increase in temperature leads to an increase in the kinetic energy of the gas molecules. As a result, the gas molecules move more rapidly and possess higher energy, making it difficult for them to adhere to the solid surface. Therefore, as the temperature increases, the adsorption of the gas decreases.

B) Enthalpy and entropy changes are negative:
This statement is correct. The process of adsorption is exothermic, meaning it releases energy. The enthalpy change (∆H) during adsorption is negative, indicating that heat is evolved during the process. Additionally, the entropy change (∆S) is negative as well, as the gas molecules become more ordered on the solid surface. These negative values for ∆H and ∆S contribute to a negative Gibbs free energy change (∆G), making the adsorption process spontaneous.

C) Adsorption is more for some specific substance:
This statement is correct. Adsorption is highly specific to the nature of the solid surface and the gas molecules involved. Different gases have different affinities for different solid surfaces. This selectivity can be attributed to factors such as intermolecular forces, surface area, and the presence of specific functional groups on the solid surface. Therefore, the adsorption of a gas on a solid can vary depending on the specific substance involved.

D) This phenomenon is reversible:
This statement is correct. Adsorption is a reversible process, meaning the adsorbed gas molecules can be desorbed from the solid surface under suitable conditions. The degree of reversibility depends on factors such as the strength of the adsorbent-adsorbate interaction, temperature, and pressure. By altering these conditions, the adsorbed gas molecules can be released from the solid surface.

In conclusion, the correct answer is option 'A' - On increasing temperature, adsorption increases. The rest of the statements are correct.