Name the noble gas atom that has the same electron configuration as each ion in the compound rubidium oxide

In rubidium oxide - Rb₂O , the ions are Rb⁺ and O²⁻
Rb is a group one element with one valence electron. To become stable it loses its outer electron to gain a complete outer shell.
Electronic configuration of Rb is - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹
Once it loses its valence electron the configuration is;
 - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 
The noble gas with this configuration is Krypton - Kr

Oxygen electron configuration is 1s² 2s² 2p⁴
Once it gains 2 electrons the configuration is  - 1s² 2s² 3p⁶
The noble gas with this configuration is Neon - Ne

The answer is !