d
In acidic medium \(M n O_{4}^{-}\) oxidises ferrous oxalate as follows:

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

\(\therefore 5\) 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 \(\mathrm{MnO}_{4}^{-}\)