Three elementary steps have been proposed for a reaction mechanism:

CHEMISTRY · Subjective · A Level · Chemistry · Introduction to organic chemistry · Introduction to organic chemistry

Problem

Three elementary steps have been proposed for a reaction mechanism: (i)

2\text{NO}_2 \rightarrow \text{N}_2\text{O}_4

(ii)

\text{NO} + \text{O}_3 \rightarrow \text{NO}_2 + \text{O}_2

(iii)

\text{NO} + \text{O} + \text{O}_2 \rightarrow \text{NO}_3

Identify which step is least plausible as an elementary reaction and briefly explain your reasoning in one sentence.