Explanation:
As the given reactions are as follows.
Step 1: [tex]NO + O_{2} \rightarrow NO_{3}[/tex] (fast)
Step 2: [tex]NO_{3} + NO \rightarrow 2NO_{2}[/tex] (slow)
As it is known that a reaction that occurs slowly helps in determining the rate of a reaction.
So, to find overall reaction we will add both step 1 and step 2 by cancelling out common species as follows.
Step 1 + 2 = [tex]NO + O_{2} + NO_{3} + NO \rightarrow 2NO_{2} + NO_{3}[/tex]
Hence, by cancelling the common species the overall reaction is as follows.
[tex]2NO + O_{2} \rightarrow 2NO_{2}[/tex]
