Answer:
C. 30.
Explanation:
Hello there!
In this case, according to the definition of the solubility, as the maximum amount of a solute that can be completely dissolved in a solvent without the formation of a precipitate, we can see that at the vertical line of 20 °C, on the KNO3 curve, we can see an intercept at about 30.
Such 30 means that just 30 grams of KNO3 will be completely dissolved in 100 g of water at 20°C, by means of its temperature dependent solubility; and therefore the answer is C. 30.
Regards!