Answer:
C. The potential energy change for a chemical reaction.
Step-by-step explanation:
The reaction coordinate q illustrates, graphically, the energy changes during exothermic and endothermic reactions. This graphical representation of the energy changes in the course of a chemical reaction is known as reaction coordinates. A reaction coordinate is a graphical sequence of steps by which the reaction progresses from reactants through activated complexes to products. Reaction coordinates explain how far a reaction has proceeded towards the products or from the reactants.
From the images attached below, we can see the reaction coordinates in the reaction profiles.