Which symbols would be included in the noble gas notation for an element that had valence electrons in the 5s subshell?

Ar

Kr

Xe

Rn

The answer is Kr (Krypton).

This is because krypton has an electronic configuration of:

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Taking note of the sequence of electronic configuration:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s

It can be seen that Kyrpton's electronic configuration finishes just before the 5s subshell. Therefore, the noble gas notation for an element with valence electrons in the 5s subshell can use [Kr] as a shortcut to denote its electronic configuration. For example:

If an element has 1 valence electron in the 5s subshell, the noble gas notation will be:

[Kr] 5s1