Question

Helium os an unreactive gas & neon is agas of extremely low reactivity.what if anything,do their atoms have in common

Answer 1

Both have the valency zero means both have filled outermost shell and are in the same group so they've same chemical property of not reacting with any element and helium has a duplet in its K shell ,while neon has an octet in its L shell. 

i hope it will help you
regards

Answer 2

refer to this attachment for the answer...