1) The s orbital can only hold two electrons
2) The arrangement does not follow the Aufbau principle
3) Ra is not a Nobel gas and can not be found at the core of an electron configuration.
The distribution of an atom's electrons among its different atomic orbitals is described by its electron configuration. The energy levels (shells) and sublevels (orbitals) that electrons occupy are commonly represented by a string of numbers and characters.
The principal quantum number (n), the sublevel letter (s, p, d, or f), and the number of electrons in that sublevel are written in a certain order.