(b)
$5C_{2}O_{4}^{2 -} + \begin{matrix}
+ 7 \\
2MnO_{4}^{-}
\end{matrix} + 16H^{+} \rightarrow 10CO_{2} + 2Mn^{2 +} + 8H_{2}O$
Equivalent weight=$\frac{molecular\ weight}{change\ in\ oxidation\ number}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{158}{5} = 31.6$