Question

what is the most likely reason that nonmetals are electrical insulators?
since valence shells are mostly empty in nonmetal atoms, the atoms attract and hold any electrons they can in order to fill their valence shells.
since valence shells in nonmetal atoms are almost full, the atoms attract electrons and hold them tightly to fill their valence shells.
since all nonmetals have valence shells that are full, they hold electrons tightly to avoid changing.
since all nonmetals have valence shells that are completely empty, they do not attract or release any electrons.

Explanation:

Non - metals are electrical insulators because their valence shells are mostly full. When valence shells are full, atoms hold electrons tightly. This tight hold means electrons are not free to move and conduct electricity.

Answer:

Since all nonmetals have valence shells that are full, they hold electrons tightly to avoid changing.