Here, substitution reaction is undergoing and the energy levels of each reaction phase is marked in graph. Its an exothermic reaction.
Step-by-step explanation:
The substitution reaction is a type of reaction where a part of a molecule is substituted by another molecule to produce 2 products.
Here in the graph, in phase A we can see two molecules are coming in a reaction and they are at a particular energy level as marked. In phase B, we can see that the molecules are undergoing the substitution reaction via SN² reaction where the energy level is higher than the original energy level because of the activation energy. The difference between the energy levels is called the activation energy which is marked as D.
The final phase is the final energy levels of these 2 products where the energy level is much lower than original energy level. So the energy is lost through the reaction as heat. So the reaction is exothermic.