What is a solution in which the molecules of solute in the solution are in equilibrium with excess undissolved molecules?

A solution in which the molecules of solute are in equilibrium with excess undissolved molecules is termed a saturated solution. In this context, saturation refers to the state where the maximum amount of solute has been dissolved in a solvent at a specific temperature and pressure, and any additional solute will not dissolve, remaining undissolved in the mixture.

In a saturated solution, dynamic equilibrium is achieved between the dissolved solute particles and the undissolved solute. This means that the rate at which solute particles dissolve is equal to the rate at which solute particles precipitate out of the solution. This characteristic is critical in various chemical and biological processes where the solute concentration is crucial for maintaining the desired conditions.

The other terms refer to different states of solutions. A dilute solution contains a small amount of solute relative to the solvent, a concentrated solution has a large amount of solute, and an unsaturated solution can still dissolve more solute. These distinctions are important for understanding solubility and the behavior of solutions in various applications.