d
Writting the half reaction oxidation half reaction

\(MnO _{4}^{-} \rightarrow Mn ^{2+}\)

balancing oxygen

\(MnO _{4}^{-} \rightarrow Mn ^{2+}+4 H _{2} O\)

balancing Hydrogen

\(8 H ^{+}+ MnO _{4}^{-} \rightarrow Mn ^{2+}+4 H _{2} O\)

balancing charge

\(5 e ^{-}+8 H ^{+}+ MnO _{4}^{-} \rightarrow Mn ^{2+}+4 H _{2} O\)

Reduction half

\(C _{2} O _{4}^{2-} \rightarrow CO _{2}\)

Balancing carbon

\(C _{2} O _{4}^{2-} \rightarrow 2 CO _{2}\)

Balancing charge

\(C _{2} O _{4}^{2-} \rightarrow 2 CO _{2}+2 e ^{-}\)

Net equation

\(16 H ^{+}+2 MnO _{4}^{-}+5 C _{2} O _{4}^{2-} \rightarrow 10 CO _{2}+2 Mn ^{2+}+8 H _{2} O\)

So \(\quad c=16\)