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.