Here we have the activation energy is the minimum energy that is needed to allow a reaction to take place. The activation energy is the energy atoms or molecules need to be in a state where they can take part in a chemical reaction or a physical transport.
In the diagram, It is the amount of energy to be added to the energy in the reactants in their initial state which is on the left plateau on the reaction-energy chart, to the transition state which is the peak of the chart.
