Read the passage carefully and answer the questions.

Sodium dichromate $Na_2Cr_2O_7$ and Potassium dichromate $K_2Cr_2O_7$, are strong oxidizing agents; in acidic solution, its oxidising action can be represented as follows:

$Cr_2{O_7}^{2-}+ 14H^++ 6e^-→2Cr^{3+}+ 7H_2O$ $(E° = 1.33V)$

The chromates and dichromates are interconvertible in aqueous solution depending upon pH of the solution. The chromate ion is tetrahedral whereas the dichromate ion consists of two tetrahedra sharing one corner with Cr-O-Cr bond angle of 126°

Potassium permanganate is prepared by fusion of $MnO_2$ with an alkali metal hydroxide and an oxidising agent like $KNO_3$. This produces the dark green $K_2MnO_4$ which disproportionates in a neutral or acidic solution to give permanganate. It is a strong oxidizing agent. Hydrogen ion concentration of the solution plays an important part in the reduction of permanganate to manganate, manganese dioxide and manganese(II) salt.

Potassium permanganate forms dark purple (almost black) crystals which are isostructural with those of $KClO_4$. The salt is not very soluble in water (6.4 g/100 g of water at 293 K), but when heated it decomposes at 513 K.

When $KMnO_4$ is added to Oxalic acid solution, the decolourisation is slow in the beginning but becomes faster after some time because

$Mn^{2+}$ acts as autocatalyst

The correct answer is Option (2) → $Mn^{2+}$ acts as autocatalyst