Identify A to E. Pyrolusite on heating with KOH in the presence of air gives a dark green compound (A). The solution of (A) on treatment with `H_2SO_4` gives a purple coloured compound `(B)`, which gives the following reactions:
(a). KI on reaction with alkaline solution of (B) changes into a compound (C).
(b). The colour of the compound (B) disappears on treatment with the acidic solution of `FeSO_4`.
(c). With conc. `H_2SO_4` compound (B) gives (D) which can compose to yield (E) and oxygen.

Explanation

Equation for the formation of (A) is :
`underset("pyrolusite")(2MnO_2) + 4KOH + O_2 to underset("potassium manganate" (A))(2K_2MnO_4) + 2H_2O`

Formation of (B):