What element has the configuration 1s2 2s2 2p6 3s2 3p6 and is a noble gas?

Answer 1

The original answer was "Oxygen".

That's not strictly correct in two ways.

First of all Oxygen is not a noble case. The noble gases are in column 8 (or zero) of the Periodic Table and all have 2p6 electronic structures. The point about the noble gases is that they have full outer shells of electrons and so don't readily react. 2p4 is not full as the p-orbitals can fill to 6.

A more correct answer is to say that 1s2 2s2 2p4 is the electronic structure for a single atom of oxygen. That said oxygen normally exists as a diatomic O2 molecule so it would have molecular orbitals.

However theoretically a 2+ ion of Neon (which is a Noble gas) would have this electronic structure. Whether it can be done is another matter.

Answer 2

This is argon, element number 18.

Answer 3

Neon.