A chloride ion (Cl-) has 8 electrons in its outermost energy level. Here's why:

* Chlorine's Atomic Structure: Chlorine has 17 electrons. Its electron configuration is 2, 8, 7. This means it has 7 electrons in its outermost energy level.

* Formation of Chloride Ion: Chlorine gains one electron to become a chloride ion (Cl-). This fills its outermost energy level, giving it a stable octet (8 electrons).