NO(g) + NO3(g) 2 NO2(g) rate kINO]INO3l 50. The reaction represented above occurs in a single step that involves the collision between a particle of NO and a particle of NO3. A scientist correctly calculates the rate of collisions between NO and NO that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy? (A) The energy of collisions between two reactant particles is frequently absorbed by collision with a third particle. particular orientation in order to react. dependent on the concentrations of the (B) The two reactant particles must collide with a (C) The activation energy for a reaction is reactant particles (D) The activation energy for a reaction is dependent on the temperature.