To an acidic solution of an anion,a few drops of $KMnO_4$ solution are added. Which of the following,if present,will not decolourise the $KMnO_4$ solution?

Among the following,identify the compound which cannot act as both an oxidizing and a reducing agent.

Identify the change in the oxidation state of the oxidising agent in the following redox reaction: $3H_3AsO_3(aq) + BrO_3^-(aq) \rightarrow Br^-(aq) + 3H_3AsO_4(aq)$

Which of the following substances acts as both an oxidizing agent and a reducing agent?

Identify the reducing agent in the following chemical equations:
$4Ag(s) + 8CN^{-}(aq) + 2H_{2}O(aq) + O_{2}(g) \rightarrow 4[Ag(CN)_{2}]^{-}(aq) + 4OH^{-}(aq)$
$2[Ag(CN)_{2}]^{-}(aq) + Zn(s) \rightarrow [Zn(CN)_{4}]^{2-}(aq) + 2Ag(s)$

In which of the following reactions does $H_2SO_4$ act as an oxidizing agent?