Which one of the following equations represent a redox reaction?

 The  equations represents a redox reaction is, $\mathrm{K}+{\mathrm{O}}_2\to {\mathrm{KO}}_2$

Redox reactions are oxidation-reduction chemical processes in which the oxidation states of the reactants change. Redox is a shortened version of reduction-oxidation. Two distinct processes—a reduction process and an oxidation process—can be used to describe all redox reactions.

$$\begin{gathered} \stackrel{0}{\mathrm{K}}+\stackrel{0}{{\mathrm{O}}_2}\to \stackrel{+1}{\mathrm{K}}\stackrel{\raisebox{1ex}{$-1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}{{\mathrm{O}}_2} \\ \stackrel{0}{\mathrm{K}}\to {\mathrm{K}}^{+}+{\mathrm{e}}^{-}\left(\mathrm{oxidation}\right) \\ 2\stackrel{0}{\mathrm{O}}+{\mathrm{e}}^{-}\to 2{\mathrm{O}}^{\raisebox{1ex}{$-1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\left(\mathrm{reduction}\right) \end{gathered}$$

K is a reducing agent and O₂ is an oxidizing agent.

Hence, correct option is C.