The correct answer is: A. Threshold energy
Threshold energy is the minimum energy required for a reaction to occur. It is the energy that must be absorbed by the reactants in order to overcome the
activation energy barrier. Once the threshold energy is reached, the reaction can proceed spontaneously.Activation energy is the energy required to form the activated complex, which is an intermediate state in a chemical reaction. The activated complex is unstable and will either decompose back to the reactants or proceed to form the products.
Free energy is a thermodynamic quantity that is used to determine whether a reaction is spontaneous or not. A reaction is spontaneous if the change in free energy is negative.
Internal energy is the total energy of a system, including the kinetic energy of its components and the potential energy of its interactions.
In conclusion, the minimum energy required for an effective collision is the threshold energy. This is the energy that must be absorbed by the reactants in order to overcome the activation energy barrier.