Answer
See the answer below.
Work Step by Step
a)
$\begin{matrix}
NO_2(g)&+&\underline{\underline{NO_2(g)}}&\rightarrow&NO(g)&+&\underline{NO_3(g)} \\
\underline{NO_3(g)}&+&CO(g)&\rightarrow&\underline{\underline{NO_2(g)}}&+&CO_2(g) \\
\hline
NO_2(g)&+&CO(g)&\rightarrow&NO(g)&+&CO_2(g)
\end{matrix}$
b) Both steps are bimolecular (two molecules exchange atoms).
c) $NO_3$ is an intermediary to this reaction since it's not a part of the global reactants or products.
