Which of the following can act both as an oxidising as well as reducing agent?

Which of the following is the strongest oxidizing agent?

$A$ solution of sulphur dioxide in water reacts with $H_2S$ precipitating sulphur. Here,sulphur dioxide acts as:

Identify the reducing agent in the following reaction:
$H_2O_{2(aq)} + ClO_{4(aq)}^{-} \rightarrow ClO_{2(aq)}^{-} + O_{2(g)}$

Which among $KI, FeSO_4, K_2MnO_4, KMnO_4$ cannot be oxidised by $O_3$?

Consider the reaction $H_2SO_{3(aq)} + Sn^{4+}_{(aq)} + H_2O_{(l)} \to Sn^{2+}_{(aq)} + HSO_4^-(aq) + 3H^{+}_{(aq)}$. Which of the following statements is correct?