Final answer:
Sodium, when it loses its single valence electron, attains a noble gas electron configuration identical to that of neon.
Step-by-step explanation:
When a sodium (Na) atom loses its single valence electron from the 3rd energy level, it forms a cation (Na+) with an electron configuration identical to that of neon, a noble gas. This is because sodium's original configuration is [Ne]3s1, and upon losing one electron, the remaining configuration is [Ne], which has eight valence electrons and fulfills the octet rule. Sodium achieves a stable electronic configuration by losing its outermost electron, which matches the configuration of noble gases that inherently have complete valence shells.