Question

which element has a complete valence electron shell?
selenium (se)
oxygen (o)
fluorine (f)
argon (ar)

Explanation:

To determine which element has a complete valence electron shell, we recall the concept of noble gases (Group 18 elements) having a full valence shell (8 electrons, except helium with 2). Selenium (Se) is in Group 16, oxygen (O) in Group 16, fluorine (F) in Group 17—all need to gain electrons to fill their shells. Argon (Ar) is a noble gas (Group 18), so it has a complete valence shell (8 valence electrons, electron configuration ends with \(3s^2 3p^6\)).

Answer:

D. argon (Ar)