Final answer:
The correct answer is Option C. Transition metals have the highest average valence electron energy.
Step-by-step explanation:
The group of elements with the highest average valence electron energy is transition metals. Transition metals are metallic elements in which the last electron added enters a d orbital. The valence electrons in transition metals include the ns and (n-1) d electrons. These elements have high average valence electron energy due to the partially filled d orbitals.