Please tell me if these are oxifation or reductive half equations?

Question

Please explain why briefly:

1) K = K+ + e-
2) H2 = 2H+ + 2e-
3)O = O2- - 2e-
4) Cu+ = Cu2+ + e-

Answer 1

These are all oxidation half-reactions. 2 ways of determining this:

1) If electrons are being listed as a product, you have oxidation.
2) All of your reactants are going up in oxidation number. Example is K going to K+ (0 --> +1)