$2 M n O_{4}^{-}+5 C_{2} O_{4}^{2-}+16 H^{+} \rightarrow$$2 M n^{2+}+10 C O_{2}+8 H_{2} O$

$\therefore 5$ moles of oxalate ions are oxidised by $2$ moles of $M n O_{4}^{-}$

$\therefore 1$ mole of oxalate ion is oxidised by

$\frac{2}{5} \text { mole of } M n O_{4}^{-}$

$=0.4$ mole of $\mathrm{MnO}_{4}^{-}$