Ease Into Prep with an MCAT^® Question of the Day

D is the correct answer.

To answer this question, recall that the slow step of a reaction is the rate-determining step. The rate is always related to the concentrations of the reactants in the rate-determining step (not the overall reaction), so NO₂ is the only compound that should be included in the correct answer. The concentration of NO₂ is squared in the rate law because the stoichiometric coefficient of NO₂ in the rate-determining step is 2.