The solubility of potassium chloride in boiling water is 56.3 g/100 g water. if you add 250.0 g of potassium chloride to 50.0 g of boiling water, will the potassium chloride all dissolve?

The solubility of KCl in boiling water is 56.3 g / 100 g water So each gram of water dissolve 56.3 / 100 = 0.563 g KCl in g water

We have here 50 g water so the total amount of KCl dissolved = 50 * 0.563 = 28.15 g KCl

We have 250 g KCl so it is not dissolved completely (only 28.15 g KCl will be dissolved)