An example of autocatalysis is

During oxidation of oxalic acid by acidified ${\mathrm{KMnO}}_4,$ ${\mathrm{Mn}}^{+2}$ is produced. This ${\mathrm{Mn}}^{+2}$ ion acts as autocatalysis.

$\underset{\mathrm{Purple}}{{\mathrm{MnO}}_4^{-}}+8{\mathrm{H}}^{+}+5{\mathrm{e}}^{-}\to \underset{\mathrm{Colorless}}{{\mathrm{Mn}}^{2+}}+4{\mathrm{H}}_2\mathrm{O}$

When potassium permanganate undergoes a reaction with acidic oxalate ions, the rate of the reaction is initially slow. But due to the formation of ${\mathrm{Mn}}^{+2}$ ions the rate slowly increases.

Therefore, option D is correct.