Why are zero group elements chemically inert ?

Explanation

(1) In group 18 elemetns, except helium (He) having electronic configuration `1s^(2)`, all other elements have completely filled valence shell. For example, `1s^(2)np^(6)` in case of remaining elements.
(2) Since they have all 8 electrons paired they have extra stability and do not have a tendency to lose or gain electrons.
(3) They have very high ionisation enthalpy.
Therefore group 18 elements are chemically inert and hence called inert elements.