The correct answer is:
Helium atoms have 2 valence electrons, while atoms of the other elements in the group all have 8 valence electrons.
This is because helium is unique among the noble gases as it has only 2 electrons and therefore only 2 valence electrons, while the other noble gases (such as neon, argon, krypton, xenon, and radon) have a complete outer shell with 8 valence electrons.