Question

What is a saturated solution? How can an unsaturated solution be changed to a saturated solution without adding any more solute to it?

Answer 1

At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution.
An unsaturated solution can become more saturated by lowering the temperature. Because the solvent vibrates less, less solution can be dissolved at once, creating a greater saturation.