Question

Calculate the solubility of KCl mol/DM³at 30oC of 20 cm³ of a saturated solution of KCl contains 4.50g of the solution.

Answer 1

20 cc contains 4.5 g KCl. How many moles is that?

mols = grams/molar mass = 4.5/74.6 = about 0.060 but you need to use a more accurate number. Then
0.060 mol x (20 cc/1000 cc) = ? mols/dm^3