When an acid solution of oxalic acid at $80°C$ is titrated with ${\mathrm{KMnO}}_4$ solution, the first few drops of ${\mathrm{KMnO}}_4$ are discolored slowly but decolorization occurs fast later. This is because

When oxalic acid reacts with ${\mathrm{KMnO}}_4, {\mathrm{Mn}}^{+2}$ is formed. Initially the reaction process is slow as because of the formation of ${\mathrm{MnO}}_4^{-}$.

When ${\mathrm{MnO}}_4^{-}$ got converted to ${\mathrm{Mn}}^{+2}$ the reaction became faster. So, due to catalytic action of ${\mathrm{Mn}}^{+2}$, discoloration took place. This implies that ${\mathrm{Mn}}^{+2}$ acts as an auto catalyst here that increases the rate of the reaction.

Hence, option (B) is correct.