Final answer:
Adding solute (solid) to an unsaturated solution causes the concentration of the solution to decrease.
Step-by-step explanation:
The addition of solute (solid) to an unsaturated solution causes the concentration of the solution to decrease. This is because when solute particles are added, they occupy some of the solvent particles, resulting in a decrease in the concentration of the solvent. As a result, the overall concentration of the solution decreases.