Concept:A saturated solution consists of undissolved solute in dynamic equilibrium with its dissolved form.
Explanation:At saturation, the rate at which the undissolved solute dissolves equals the rate at which the dissolved solute crystallises.
This dynamic equilibrium is established between the dissolved solute and the undissolved solute.
The solvent only provides the medium in which dissolution occurs, so it is not one of the equilibrating species.
When the temperature of the saturated solution changes, the value of the solubility changes and this equilibrium gets disturbed.
To restore equilibrium, the system either dissolves more solute or precipitates some solute until a new saturation point is reached.
Therefore, the equilibrium in a saturated solution is between the dissolved solute and the undissolved solute.
Answer:C. Dissolved solute and the undissolved solute