In an acidic medium,when $KMnO_4$ is reduced by oxalic acid,what is the change in the oxidation state of $Mn$?

In the reaction $H_2S + NO_2 \to H_2O + NO + S$,$H_2S$ is

Observe the following reaction:
$2 KClO_{3(s)} \xrightarrow{\Delta} 2 KCl_{(s)} + 3 O_{2(g)}$
In this reaction:

Identify the redox couples involved in the following reactions:
$(a) \ Cu + Zn^{+2} \to Cu^{+2} + Zn$
$(b) \ Mg + Fe^{+2} \to Mg^{+2} + Fe$
$(c) \ Br_{2} + 2Cl^{-} \to Cl_{2} + 2Br^{-}$
$(d) \ Fe + Cd^{+2} \to Cd + Fe^{+2}$

Which of the following is not true for oxidation?

In which of the following reactions does the oxidation of nitrogen occur?