Answer
$Rate= k[NO_{3}][O_{2}]^{2}$
Work Step by Step
Recall that for a general reaction
$aA+bB \rightarrow cC+dD$,
$Rate= k[A]^{x}[B]^{y}$ where x and y represent the order with respect to the reactants A and B respectively.
Therefore, rate law for the given reaction is
$Rate= k[NO_{3}][O_{2}]^{2}$
