Physical adsorption of a gaseous species may change to chemical adsorption with

Increase in temperature

The correct answer is 2. Increase in temperature.

Physical adsorption and chemical adsorption are two different types of adsorption processes that occur at the surface of a material.

Physical adsorption (also known as physisorption) involves weak van der Waals forces or London dispersion forces. This type of adsorption is usually reversible and occurs at lower temperatures. It is primarily influenced by factors like temperature and pressure.

Chemical adsorption (also known as chemisorption) involves the formation of chemical bonds between the adsorbate and the adsorbent. This type of adsorption is typically stronger and more specific than physical adsorption. It often requires higher temperatures and is more influenced by the nature of the adsorbent and adsorbate.

Now, let's consider the given options:

1. Decrease in temperature: This would generally favor physical adsorption, as lower temperatures typically enhance physisorption.

2. Increase in temperature: This would generally favor chemical adsorption, as higher temperatures are often required for the activation of chemical reactions and the formation of chemical bonds.

3. Increase in surface area of adsorbent: This would generally favor physical adsorption because a higher surface area provides more sites for weak van der Waals forces to act.

4. Decrease in surface area of adsorbent: This would generally favor chemical adsorption because chemical adsorption often involves specific sites on the surface of the adsorbent.

Based on this analysis, the correct answer is: Increase in temperature (Option 2): This condition is more likely to favor the transition from physical adsorption to chemical adsorption.