Final answer:
Silicon (Si) has electrons in three energy levels with an electron configuration of Si: 1s² 2s² 2p¶ 3s² 3p², indicating that its valence electrons are in the third energy level.
Step-by-step explanation:
The element with electrons in three energy levels is Silicon (Si). Atoms with more than ten electrons require more than two shells, and elements occupying the third and subsequent rows of the periodic table have electrons in the third energy level. Silicon has 14 electrons with the following electron configuration: Si: 1s² 2s² 2p¶ 3s² 3p². This shows that the highest energy electrons for Silicon are in the third energy level (n=3).
As additional examples, Lithium (Li) has its outermost electrons in the second energy level with an electron configuration of Li: 1s² 2s¹. Scandium (Sc) also has electrons in three energy levels, but since the student's question asks for elements with exactly three energy levels, Scandium would not be correct as it also has electrons starting to fill the fourth energy level due to its d-sublevel electrons.