In the Following Reaction, NO₃ Molecule Does Not Appear in the Balanced

In the following reaction, NO₃ molecule does not appear in the balanced chemical equation for the overall reaction. This indicates that NO₃ is a(n) _____ in the reaction. $$\begin{array} { c } \mathrm { NO } _ { 2 } + \mathrm { NO } _ { 2 } \longrightarrow \mathrm { NO } _ { 3 } + \mathrm { NO } \\\mathrm { NO } _ { 3 } + \mathrm { CO } \rightarrow \mathrm { NO } _ { 2 } + \mathrm { CO } _ { 2 } \\\hline\mathrm { NO } _ { 2 } + \mathrm { CO } \rightarrow \mathrm { NO } + \mathrm { CO } _ { 2 }\end{array}$$

A) intermediate
B) micelle
C) adduct
D) polymer
E) emulsion