The balanced equation of potassium permanganate and oxalic acid reaction in acidic medium is shown below.
2KMn+7O4+5H2C2+3O4+3H2SO4(dil.)→K2SO4+2M+2nSO4+10C+4O2+8H2O
The initial oxidation state of carbon in the oxalic acid is +3. The oxidation state of carbon at the end point is +4(in carbon dioxide). Hence, the change in oxidation state of carbon at the end point is 1.