Molarity balance equation of the reaction suggests that 1 mole of KMNo4 completely oxidized 5 moles of ferrous ammonium sulphate

KMnO4 + FeC2O4 + H ------> Mn2+  + Fe3+  +  2CO2

KMnO4  = 5 electrons

ferrous oxalate in acidic solution = 3 electrons

while reaction exchange of electrons takes place..........so

3 moles of KMnO4 = 5 moles of  FeC2O4

5 moles of  FeC2O4 = 3 moles of KMnO4

so 1 mole of FeC2O4 = 3/5 moles of KMnO4

hence 3/5 moles of KMnO4 of KMnO4 will be needed to react completely with one mole of ferrous oxalate in acidic solution.....