In this case, since the potential energy versus reaction progress diagrams are related to the energetic profile of a chemical reaction, we can set the initial point at the beginning of the reaction as the energy of the reactants and the final point as the energy of the products.
Next, since the change in the enthalpy of a reaction is quantified by subtracting products minus reactants, we can see that the products have less energy than the reactants and therefore ΔH for this reaction is negative, which matches with the definition of D. Exothermic reaction.
