Why do helium, neon and argon have a zero valency?

Why do not helium, neon and argon form chemical compounds.

Why do Beryllium and nitrogen have zero electron affinity ?

Fluorine, helium, neno, argon

Which elements have zero valency?

Why do inert gases have zero valency value ?

(a) Why does helium have zero valecy? (b) Name the secientist and his experiment to prove that nucleus of an atom is positively charged.