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

The element that has a complete valence electron shell is

Argon(Ar)

Argon is in group 18 and period three in the periodic table. Therefore Argon electronic configuration is 2.8.8 or 1s^2 2s^2 2P^6 3S^2 3P^6 or [Ne] 3s^2 3p^6. The valence electrons of Argon is 3s^2 3p^6 which are completely filled since an 3S subshell can hold a maximum of 3 electrons while a 3P subshell can accommodate a a maximum of 6 electrons hence, Argon has a complete filled valence shell.

the electron configuration that you gave me has 16 electrons ergo it has 16 protons ergo it is the element sulfur.