Final answer:
Neon (Ne) is the element with a complete outermost energy level, fulfilling the octet rule and making it stable as a noble gas.
Step-by-step explanation:
The element from the table that has a complete outermost energy level is neon (Ne). Neon has an electron configuration of 1s²2s²2p⁶, which means it has two electrons in its first energy level and eight in the second, fulfilling the octet rule. This makes neon's outermost energy level full, giving it stability as a noble gas. In contrast, the electron configuration of sodium (Na) is 1s²2s²2p⁶3s¹, indicating that sodium has one valence electron in its third energy level, which it can lose to achieve a noble gas configuration similar to neon.