What element is being oxidized in the following redox reaction?
mno4 (aq) + h2c2o4(aq) → mn2+(aq) + co2(g)

C is the element thats has been oxidized.

Explanation:

MnO₄⁻ (aq)  +  H₂C₂O₄ (aq)  →  Mn²⁺ (aq)  +  CO₂(g)

This is a reaction where the manganese from the permanganate, it's reduced to Mn²⁺.

In the oxalic acid, this are the oxidation states:

H: +1

C: +3

O: -2

In the product side, in CO₂ the oxidation states are:

C: +4

O: -2

Carbon from the oxalate has increased the oxidation state, so it has been oxidized.