To know which has the highest concentration or molarity of potassium ion, all we have to do is to calculate based on stoichiometry.
Concentration of potassium in KCl:
molarity K in KCl = (0.20 moles KCl / L) (1 mole K / 1 mole KCl) = 0.20 M
Concentration of potassium in K2CrO4:
molarity K in K2CrO4 = (0.15 moles K2CrO4 / L) (2 mole K / 1 mole K2CrO4) = 0.30 M
Concentration of potassium in K3PO4:
molarity K in K3PO4 = (0.08 moles K3PO4 / L) (3 mole K / 1 mole K3PO4) = 0.24 M
Therefore 0.15M K2CrO4 has the highest K ion concentration.
