The reaction occurs through three elementary steps with energy changes:

Step (i): is endothermic ( ), so B has higher energy than A , creating the first peak.
Step (ii): is exothermic ( ), so C has lower energy than B , creating a lower second peak.
Step (iii): is exothermic ( ), so D has lower energy than C , creating an even lower third feature.

Overall reaction: Since step (i) is endothermic and steps (ii) and (iii) are exothermic, the reaction can be endothermic overall depending on the magnitudes. The overall energy change is positive ( is endothermic), meaning D must be at higher energy than A .
The reaction profile must show three distinct peaks/steps with the final product D positioned higher than the initial reactant A .
correctly depicts this three-step mechanism with proper energy relationships and overall endothermic character.