Question

Elements of group 18are called zerovalent

Answer 1

Yes,elements of group 18 are called zero valent groups because of absence of free electrons in their orbitals.All the electrons in their shells have a completed octed or a duplet(Helium). They are the most stable and are very rare due to their non reactive nature.It is this absence of free electrons available dor reaction which makes them to be grouped in zero valent or inert gas or rare gas elements

Answer 2

yes because elements in group 18 are noble gases and they cannot gain or loses electrons