[Rn] 7s²

Here's a breakdown:

* [Rn] represents the electron configuration of the noble gas radon, which is the element preceding radium on the periodic table. This shorthand notation helps simplify the configuration.

* 7s² indicates that there are two electrons in the 7s orbital.

This configuration reflects the fact that radium is in the second column (group 2) of the periodic table, meaning it has two valence electrons in its outermost shell.