Adsorption is used in separation processes because molecules what?

• A. Dissolve in a liquid
• B. Adhere to a solid surface
• C. React with a catalyst
• D. Evaporate

Answer: (B)

Molecules separate because some prefer to stick to a solid surface more than others. Adsorption uses this tendency: the fluid's components interact with and attach to the surface of a solid (like activated carbon or a chromatography stationary phase). As the fluid passes by, species with higher affinity for the surface are held back, while those with weaker affinity move through, leading to separation. This surface-based retention is the key difference from other processes.

Dissolving in a liquid involves the bulk phase, not surface attachment, so it doesn’t create the same selective retention. Reacting with a catalyst changes the chemical species rather than simply adsorbing them. Evaporating involves a phase change to vapor, again not about surface adhesion.