Why doesn't potassium ion K+ from KMnO4 appear in the following two unbalanced equations:

MnO4– + C2O42– --> Mn2+ + CO2
MnO4– + Fe2+ --> Mn2+ + Fe3+ ?

is it because K+ is just a spectator ion or is it because K+ would cause a net positive charge in the products

The potassium ion is a spectator ion on both side.

And as a follow up, adding K^+ to each side in the balanced equations will NOT cause a positive charge (in excess, anyway). The positive charges will balance the negative charges on each side of the equation.

A. K+ is a spectator ion and redox reactions are written as net ionic reactions.

B. KMnO4 is not added to either reaction.

C. The equations cannot be balanced if the potassium ion K+ is present.

D. The presence of K+ would result in a net positive charge in the products.

E. None of these.

so the answer would definately be none of these then right?

A. K+ is a spectator ion and redox reactions are written as net ionic reactions.
K+ is a spectator ion and redox reactions MAY be written as net ionic reactions BUT they may also be written as molecular equations.

B. KMnO4 is not added to either reaction.

definitely not correct.

C. The equations cannot be balanced if the potassium ion K+ is present.

K+ may be added AND the equation can be balanced.

D. The presence of K+ would result in a net positive charge in the products.

definitely not correct.

E. None of these.

so the answer would definately be none of these then right?
right. I would go with E. A comes close but redox reactions can be balanced if written as an ionic equation or if written as a molecular equation.