Question

the amount of energy needed to start a reaction
substrate
optimal ph
activation energy
protein

Explanation:

The question is about the term for the energy needed to start a reaction. In biology (a subfield of Natural Science), activation energy is defined as the minimum energy required to initiate a chemical reaction. Substrate is the substance a reaction acts on, optimal pH is a condition for enzyme activity, and protein is a macromolecule; none of these match the definition of the energy to start a reaction. So the correct option is Activation Energy.

Answer:

Green box: Activation Energy