Which of following is NOT a redox reaction?

What is the change in oxidation number of nitrogen in following conversion?

$$\mathrm{NO}_3^{-} \longrightarrow \mathrm{NO}_2$$

Identify reducing agent in following reaction

$$\mathrm{H}_2 \mathrm{O}_{2(\mathrm{ag})}+\mathrm{ClO}_{4(\mathrm{aq})}^{-} \rightarrow \mathrm{ClO}_{2(\mathrm{aq})}^{-}+\mathrm{O}_{2(\mathrm{g})}$$

Identify reductant in following reaction.

$$\mathrm{H}_2 \mathrm{~S}+\mathrm{NO}_2 \rightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{NO}+\mathrm{S}$$