When water molecules surround a dissolved ion, which term best describes this interaction?

The term that best describes the interaction when water molecules surround a dissolved ion is a hydration shell. In biological and chemical contexts, when an ion dissolves in water, the polar water molecules are attracted to the charged ion. The positive and negative ends of the water molecule interact with the ion, forming a structured layer of water molecules around it, which is known as the hydration shell. This shell stabilizes the ion in solution, preventing it from re-associating with other ions of the same charge, and plays a crucial role in processes such as cellular function and chemical reactions in aqueous environments.

While the solvation state can refer to the process of surrounding solute particles with solvent molecules, it is broader in context and not specific to water. Cohesive effect pertains to the attraction between water molecules themselves, while dispersal layer is not a standard term used to describe this specific interaction in the context of solvation. Thus, hydration shell is the most precise and relevant term here.