What are the oxidation numbers of potassium, sulfur, and oxygen, respectively, in k2so4?

In potassium sulfate (K₂SO₄):

1) potassium has oxidation number + 1, because it is metal in first group of Periodic table of elements.

2) sulfur has oxidation number + 6.

3) oxygen has oxidation number - 2, because it gain electrons from potassium and sulfur.

Compound has neutral charge: + 1· 2 + 6 + (-2) · 4 = 0.