There are several examples, which reveal that the surface of a solid has the tendency to attract and retain the molecules of the phase with which it comes into contact. These molecules remain only at the surface and do not go deeper into the bulk. The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed adsorption. The molecular species or substance, which concentrates or accumulates at the surface is termed adsorbate and the material on the surface of which the adsorption takes place is called adsorbent.

Adsorption is essentially a surface phenomenon. Solids, particularly in finely divided state, have large surface area and therefore, charcoal, silica gel, alumina gel, clay, colloids, metals in finely divided state, etc. act as good adsorbents.

Which of the following can result in a transition from physisorption to chemisorption?

Increase in temperature

The correct answer is option 2. Increase in temperature.

Out of the listed options, the factor that can lead to a transition from physisorption to chemisorption is: 2. Increase in temperature

Physisorption: This is a weak physical adsorption where molecules are held on a surface by weak Van der Waals forces. It typically occurs at lower temperatures.

Chemisorption: This is a stronger chemical adsorption where molecules form chemical bonds with the surface atoms. It usually requires higher energy input.

Increasing the temperature provides the activation energy needed for the adsorbed molecules to overcome the weak Van der Waals forces and interact more closely with the surface, potentially forming chemical bonds. This transition from physisorption to chemisorption can alter the properties of the adsorbed layer and the overall interaction between the molecule and the surface.

Let us look the other options:

Decrease in temperature: Generally, lower temperatures favor physisorption due to weaker thermal motion of the molecules.

Decrease in pressure: While pressure can affect the amount of gas adsorbed, it doesn't directly influence the type of adsorption (physisorption vs chemisorption).

Increase in surface area: A larger surface area can provide more sites for adsorption, but it doesn't directly influence the strength of the adsorption (physisorption vs chemisorption).

The transition from physisorption to chemisorption depends on various factors specific to the system, including the nature of the adsorbate (molecule being adsorbed), the adsorbent (surface), and the overall activation energy required. Increasing temperature may not always be sufficient to induce chemisorption for a particular system.