2 mole, equimolar mixture of Na2C2O4 and H2C2O4 required V1 L of 0.1 M KMnO4 in acidic medium for complete oxidation. The same amount of the mixture required V2 L of 0.1 M NaOH. The ratio of V1 to V2 is:
a. 2 : 1
b. 4 : 5
c. 5 : 4
d. 2 : 5