The energy profile for the conversion of species X to species Z shows three distinct energy maxima separated by two minima, and the products are at a lower energy than the reactants. Four possible mechanisms are proposed.
I. X → Y (slow) Y → Z (fast)
II. X → A (fast) A → B (slow) B → Z (fast)
III. X + M → C (fast) C → D (slow) D → E (slow) E + M → Z (fast)
IV. X ⇌ F (fast equilibrium) F → Z (slow)
Which mechanism is most consistent with the energy profile?
a) I only
b) III only
c) II only
d) II and III