Adsorption is the phenomenon of attracting and retaining the molecules of a substance on the surface of a solid resulting into a higher concentration on the surface than in the bulk. The substance adsorbed is known as adsorbate and the substance on which adsorption takes place is called adsorbent. In physisorption adsorbate is held to the adsorbent by weak van der Waals forces and in chemisorption by strong chemical bond.

The process of absorption is accompanied by

Increase in entropy

The correct answer is option 1. Increase in entropy.

Let us delve into each of the options:

1. Increase in Entropy: Entropy is a measure of the disorder or randomness of a system. When a substance is absorbed into another substance, the molecules of the absorbing material rearrange themselves to accommodate the absorbed molecules. This rearrangement often leads to an increase in disorder within the system. For example, in the case of a gas being absorbed by a liquid, the gas molecules become dispersed throughout the liquid, leading to an increase in randomness. This increase in disorder corresponds to an increase in entropy. Therefore, absorption processes typically result in an increase in entropy.

2. Decrease in Entropy (Incorrect Option): A decrease in entropy would imply a decrease in disorder or randomness, which is not observed during absorption processes. Therefore, Option 2 is incorrect.

3. Increase in Enthalpy: Enthalpy is a measure of the total heat content of a system at constant pressure. While absorption processes may involve energy changes, such as heat being released or absorbed, there is no inherent requirement for enthalpy to increase during absorption. The change in enthalpy during absorption depends on various factors such as the nature of the absorbing material, the absorbed substance, and the conditions of the process.

4. Increase in Gibbs Free Energy (Incorrect Option): Gibbs free energy is a thermodynamic potential that combines enthalpy and entropy to predict whether a reaction will be spontaneous. However, the increase in disorder (entropy) during absorption typically results in a decrease in Gibbs free energy, making the process more favorable or spontaneous. Therefore, an increase in Gibbs free energy is not expected during absorption.

In summary, absorption processes are generally accompanied by an increase in entropy due to the increased disorder within the system. This leads to a more favorable change in Gibbs free energy, making the process spontaneous.