In a volumetric analysis experiment, a solution of sodium oxalate (Na2C2O4) in acidic solution is titrated with a solution of potassium permanganate (KMnO4) according to the following balanced chemical equation: 2KMnO4(aq) + 8H2SO4(aq) + 5Na2C2O4(aq) → 2MnSO4(aq) + 8H2O(l) + 10CO2(g) + 5Na2SO4(aq) + K2SO4(aq). It required 40.0 mL of 0.0335 M KMnO4 to reach the endpoint. What mass of Na2C2O4 was present initially?
a) 11.2 g
b) 0.0718 g
c) 0.448 g
d) 1.79 g