What is the formula unit of the ionic compound formed from:

A. Na⁺¹ and NO₃^-1

B. K⁺¹ and PO₄^-3

C.NH₄⁺¹ and S^-2

D. Ca⁺² and CO₃^-2

E. Mg⁺² and OH^-1

F. Al⁺³ and SO₄^-2