Which of the following is a true statement?

In the redox reaction $2MnO_4^- + 5C_2O_4^{2-} + 16H^{+} \rightleftharpoons 2Mn^{2+} + 10CO_2 + 8H_2O$,the ion acting as autocatalyst is

For the reaction $4Fe + 3O_2 \to 4Fe^{3+} + 6O^{2-}$,which of the following statements is incorrect?

The number of moles of $KMnO_4$ required to oxidize one equivalent of $KI$ in the presence of sulphuric acid is

Which of the following reactants can be reduced by $SO_2$ in the given reactions?
$(I)$ $O_3 \to$ product
$(II)$ $Cr_2O_7^{2-} \xrightarrow{H^{+}} $ product
$(III)$ $MnO_4^{-} \xrightarrow{H^{+}} $ product
$(IV)$ $H_2S \to$ product

$K_2Cr_2O_7$ paper acidified with dilute $H_2SO_4$ turns green when exposed to