Which species does not have a noble gas electron
configuration?
(1) na+ (3) ar
(2) mg2+ (4) s

Noble gases are elements with complete octet configuration

this means their outershells are complete with 8 electrons

other elements have incompletely filled outershells therefore they either lose or gain electrons to gain a complete octet in the outershell

1. Na⁺ - Na electron configuration is 2,8,1

positive charge means it loses its outermost shell electron and becomes 2,8 with 8 electrons in the outermost shell

therefore has a noble gas configuration

2.Mg²⁺ - Mg electron configuration is 2,8,2

2 plus means Mg loses 2 electrons in the outermost shell and becomes 2,8 and has 8 electrons in the outer energy shell

therefore has a noble gas configuration

3.Ar - Ar electron configuration is 2,8,8

Ar has 8 electrons in the outermost energy shell therefore its complete

Ar element is a noble gas

4.S - S electron configuration is 2,8,6

S has 6 electrons in the outermost energy

therefore it does not have a noble gas configuration

correct answer is 4) S