Final answer:
If the solution of 40 g KNO3 in 100 g of water at 40°C is saturated, unsaturated, or supersaturated, you must compare the amount dissolved with the known solubility at that temperature, which requires consulting a solubility curve for KNO3.
Step-by-step explanation:
When 40 g of KNO3 are dissolved in 100 g of water at 40°C, to determine whether the solution is saturated, unsaturated, or supersaturated, we refer to the solubility curve of KNO3. A saturated solution is one where the maximum amount of solute that can dissolve in the solvent at a given temperature has been added. An unsaturated solution contains less solute than the maximum that could be dissolved at that temperature. A supersaturated solution contains more solute than what is typically soluble at that temperature, often achieved by first dissolving at a higher temperature and then cooling.
For KNO3 at 40°C, if we compare the amount dissolved to the known solubility at that temperature (not provided here), we could categorize the solution. For example, if the solubility at 40°C were 50 g per 100 g of water, 40 g would represent an unsaturated solution. If the solubility were 35 g, this would be a saturated solution as it's at the limit of solubility with no excess. If no additional KNO3 could dissolve in the solvent, any additional would lead to the excess remaining undissolved, indicating the solution is saturated.