Elements that have complete valence electron shells are mostly found in the:

• A. halogens
• B. transition metals
• C. alkali metals
• D. noble gases

Answer: (D)

Verified step by step guidance

1. Understand that elements with complete valence electron shells are chemically stable and generally unreactive.
2. Recall the periodic table groups and their typical valence electron configurations: halogens have 7 valence electrons, alkali metals have 1, transition metals have variable valence electrons.
3. Recognize that noble gases are the group of elements that naturally have full valence electron shells, typically 8 electrons (except helium with 2).
4. Identify that this full valence shell configuration makes noble gases very stable and mostly inert compared to other groups.
5. Conclude that elements with complete valence electron shells are mostly found in the noble gases group.