they are lighter than air. they have full outer electron shells. they have excess electrons to share. they easily react with other elements.
On the periodic table, the elements in group 18 (8A) (helium, neon, argon, etc.) are grouped together because

Options:
- they are lighter than air.
- they have full outer electron shells.
- they have excess electrons to share.
- they easily react with other elements.

they have full outer electron shells.