Chapter 5, Problem 42RQ

One pollutant in smog is nitrogen dioxide. ${\text{NO}}_{\text{2}}$. The gas has a reddish brown color and is responsible for the red- brown color associated with this type of air pollution. Nitrogen dioxide is also a contributor to acid rain because when rain passes through air contaminated with ${\text{NO}}_{\text{2}}$, it dissolves and undergoes the following reaction:

${\text{3NO}}_{\text{2}}\left(g\right){\text{ + H}}_{\text{2}}\text{O }\stackrel{}{\to }\text{NO}\left(g\right){\text{ +2H}}^{\text{+}}\text{(}aq{\text{)+ 2NO}}_3^{-}\left(aq\right)$

In this reaction, which element is reduced and which is oxidized? Which is the oxidizing agent and which is the reducing agent?