What is the process called when dissolved ions reform an undissolved solid?

The process in which dissolved ions reform an undissolved solid is known as precipitation. This occurs when the concentration of certain ions in a solution exceeds their solubility, leading them to become supersaturated and subsequently form a solid phase. This solid, known as a precipitate, can then settle out of the solution.

Precipitation is an important concept in various chemical processes, including reactions in solution and analytical chemistry, where it is often used to separate compounds. For example, mixing two clear solutions containing different ions can lead to the formation of a solid that can be filtered out, providing a means to isolate specific components from a mixture.

In observing the other options: dissolution refers to the process where a solid solute dissolves into a solvent to form a solution; evaporation involves the transition of a liquid to a gas, typically as a result of heat; and condensation is the reverse process of evaporation, where gas molecules lose energy and transition back to the liquid state. None of these processes involve the formation of an undissolved solid from dissolved ions, which reinforces why precipitation is the correct terminology in this context.