Answer:
argon (Ar)
Step-by-step explanation:
Argon is the element from the given choices with a complete valence electron shell.
The valence electron shell is the outermost shell of an atom.
- Elements with complete outermost shell are found in the 8th group on the period table.
- In the 8th group, the elements are generally inert and unreactive.
- Elements with this configuration have 8 electrons in their outermost shell and 2 for helium.
- Some of the elements in this group are Helium and Neon