1. Student 2 is correct.
2. In fact the reaction takes place in 2 steps. They are,
According to the law of chemical kinetics, the rate of a reaction is determined by the slowest step. Here step 1 is the slowest step i.e., rate determining step. By the law of mass action, rate of a chemical reaction is directly proportional to the product of molar concentration of the reactants. rate = k[NO2][NO2]= k[NO2]2