Answer:
Reactants, Activation energy, Energy released by the reaction and Products
Step-by-step explanation:
This energy profile is that of an exothermic reaction. In an exothermic reaction, heat is liberated to the surrounding. The surrounding becomes hotter than the environment.
The first box to the left is the reactants which signifies the species combining together.
The topmost box is the activation energy which is the energy barrier that must be over come before a reaction takes place.
The box underneath is the energy change. Here, energy is being released.
The right most box is the product of the reaction.