Which cahracteric of zero group element is common?

Which characteristic of zero group elements is common :

Oxidation state of zero group elements is

Why zero group elements are inert ?

The chemistry of zero group elements is little known because

Why are zero group elements chemically inert ?

What are zero group elements ? Give the electronic configuration of the first four of them. Why zero group elements are also known as inert gases ?

What is the common characteristic of the elements of the same group in the periodic table ?