Final answer:
The process where a pellet of KOH absorbs moisture from the air until it dissolves is called deliquescence. This is different from hydration, sublimation, and efflorescence, which refer to moisture attachment, solid to gas transition, and salt crystallization, respectively. Option B is the correct answer.
Step-by-step explanation:
When a pellet of KOH is inadvertently left on the bench, it absorbs moisture from the air until it dissolves in the excess water. This phenomenon is described by several terms that refer to different physical processes: hydration, deliquescence, sublimation, and efflorescence.
Hydration is the process where water molecules attach to a solute particle. If we consider what happens at the microscopic level when a solid like KCl is added to water, ion-dipole forces attract the ends of the polar water molecules to the potassium and chloride ions, reducing the interionic forces that bind the ions together in the crystal lattice. This lets the ions dissolve into the water as solvated ions.
Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. This is the correct answer to the question posed. Deliquescent substances often turn into a liquid as they absorb water vapor from the air.
Sublimation refers to the phase transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase, and is not applicable to the situation described with the KOH pellet.
Lastly, Efflorescence is the process where water-soluble salts crystallize out of a solution onto the surface, typically observed when water evaporates from a porous material and leaves the salts behind.
Given the description of the pellet of KOH absorbing moisture and dissolving, the correct term for the phenomenon is deliquescence.