Answer:
7,38 g of K₃PO₄
Explanation:
Molarity is an unit of chemical concentration. 0,139 M means 0,139 moles of solute per liter of solution.
In this case, the solute is potassium phosphate (K₃PO₄; molar mass: 212,27 g/mol) and the volume of the solution must be 250mL≡0,25L.
Thus, the moles of potassium phosphate you need are:
0,139 mol/L×0,25L = 0,03475 moles of K₃PO₄
In grams:
0,03475 moles of K₃PO₄ × = 7,38 g of K₃PO₄
I hope it helps!