Absorption is a bulk phenomena in chemical engineering.

Absorption:
Absorption is the process by which one substance is taken up by another substance in bulk. It involves the transfer of one or more components from a gas phase into a liquid phase. In chemical engineering, absorption is widely used in various processes such as gas treatment, separation, and purification.

Key Points:
- Absorption is a bulk phenomena.
- It involves the transfer of one or more components from a gas phase into a liquid phase.
- Widely used in gas treatment, separation, and purification processes.

Physical Adsorption:
Physical adsorption, also known as physisorption, is a surface phenomenon where molecules or atoms adhere to the surface of a solid or liquid. It is a reversible process and occurs due to weak van der Waals forces between the adsorbate and the adsorbent. Physical adsorption is not considered a bulk phenomena as it occurs at the surface.

Chemical Adsorption:
Chemical adsorption, also known as chemisorption, is a process where the adsorbate forms a chemical bond with the adsorbent surface. It involves strong chemical interactions and is typically irreversible. Chemical adsorption is also not considered a bulk phenomena as it occurs at the surface.

Sorption:
Sorption is a term used to describe both absorption and adsorption processes. It is a general term that encompasses both bulk phenomena and surface phenomena. While absorption and adsorption are specific processes, sorption is a more general term that can refer to either bulk or surface phenomena depending on the context.

Conclusion:
Of the given options, absorption is the only bulk phenomena. Physical adsorption and chemical adsorption are surface phenomena, while sorption is a general term that can refer to either bulk or surface phenomena. Absorption is widely used in chemical engineering for various gas treatment, separation, and purification processes.