21. Basically you are making a saturated solution, then cooling it which decreases the solubility and solid potassium chromate will precipitate. So, look at your graph at 60 degrees C, the solubility is 40 g K2Cr2O7 / 100 mg water, since you started with 100 g K2Cr2O7 and 200 g water, you actually have 80 g in 200 g water and 20 grams left over as solid in bottom of beaker. Then it says the solution is poured off (decanted) into a new beaker so you have a saturated solution of 80 g K2Cr2O7 in 200 g water, and you left the 20 g solid in the original beaker. Now you cool that solution down to 20C. Again, look at solubility on graph which is about 7.5g/100 g water, therefore with 200 g water that means your solution contains about 15 g of K2Cr2O7 and 25 g should precipitate (40g @40C minus 15g @20C =25 g precipitate. or 24 g which is A.