Which among the following is NOT a characteristic of Physisorption?

The correct answer is option 1. It is irreversible.

The characteristic of Physisorption that does NOT apply is : it does not require any activation energy.

Physisorption, also known as physical adsorption, is the adsorption of gas or liquid molecules onto a solid surface through weak van der Waals forces. While it occurs spontaneously without the need for additional energy, there is still a minimal activation energy required for molecules to overcome repulsive forces and approach the surface. Therefore, option 4 is not a characteristic of physisorption.