Final answer:
To determine the grams of KNO₃ needed to saturate 200 grams of water at 70°C, we need the specific solubility information from the solubility curve at that temperature.
Step-by-step explanation:
To determine how many grams of KNO₃ would be needed to saturate 200 grams of water at 70°C, we can refer to the given solubility curve. However, since the solubility curve information provided does not include the specific solubility of KNO₃ at 70°C, we cannot give a direct answer. If the solubility curve for KNO₃ at 70°C is available, we can use it to find the saturation point and determine the grams of KNO₃ needed.