Question

Why do Helium, Neon and Argon have zero valency?

Answer 1

Helium has two electrons in its only energy shell. Argon and Neon have 8 electrons each in their valence shells. As the elements have the maximum number of electrons in their valence shells (thereby achieving stable duplet and octet configurations), they do not have any tendency to combine with other elements. Hence, Helium, Neon, and Argon have zero valency.