Final answer:
On a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis, the activation energy is lower.
Step-by-step explanation:
On a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis, the activation energy is lower. This is because enzymes lower the energy barrier required for the reaction to proceed, making it easier for the reaction to take place.
For example, in a reaction without an enzyme, the activation energy represents the energy required for the reactants to reach the transition state. However, when an enzyme is present, it can form a covalent bond with the substrate, which stabilizes the transition state and reduces the activation energy.
Therefore, the correct answer is a) Lower activation energy.