Final answer:
Lowering the free energy in the transition state of a reaction increases the reaction rate by reducing activation energy.
Step-by-step explanation:
The correct answer is C) Activation energy reduction. Lowering the free energy in the transition state of a reaction increases the reaction rate because it reduces the activation energy required for the reaction to occur. The transition state is the state that a reaction must pass through in order to go from reactants to products. By lowering the energy required to reach the transition state, the reaction can proceed more easily and at a faster rate.