Final answer:
The activated complex or transition state is at the highest energy during an endothermic chemical reaction.
Step-by-step explanation:
The highest energy during an endothermic chemical reaction is found in the activated complex or transition state. The activated complex is a short-lived, unstable intermediate species that forms between the reactants and products. It is at the highest energy point in the reaction because it represents the breaking and formation of chemical bonds. The activation energy, which is the energy required to reach the transition state, is always positive, regardless of whether the reaction is exergonic or endergonic.