The correct option is D k2(k1k−1)
Slow step is the rate determining step (RDS) and (N2O2) is the reactive intermediate.
∴r=k2[N2O2][O2]
From reversible reaction, [N2O2] is:
k1k−1=[N2O2][NO2]
Substitute [N2O2] in equation (i),
r=k2(k1k−1)[NO]2[O2]
Hence, rate constant = k2(k1k−1)