Question

as additional KNO3(s) is added to a saturated solution of KNO3 at constant temperature, the concentration of the solution? (I know it remains the same but why??)

Answer 1

If it's saturated, it means that you have reached the maximum of KNO3 that can be dissolved in tour solution. Hence, if you add more solid KNO3, if won't dissolved, and will just fall at the bottom; as a result, the concentration in dissolved KNO3 will remain the same.