Final answer:
The activation energy is the minimum energy needed to initiate a reaction, represented by the energy barrier that reactants must overcome to become products.
Step-by-step explanation:
The activation energy of a reaction is c) The minimum energy required to initiate a reaction. This energy is the barrier or threshold that particles in a reaction must overcome in order to react when they collide. It's analogous to a hill that reactants need to climb so that they can 'roll down' to become products.
The activation energy can be viewed on a potential energy diagram as the height of the hill between reactants and products. The higher the activation energy, the slower the reaction tends to be, since fewer molecules will have sufficient energy to overcome this barrier.