[Rn] 7s2 is the noble gas notation for radium. A link is provided to the Wikipedia article on radium.
Ra, radium
[Rn] 5f9 7s2
[Rn] 7s2 5f1
The electron configuration of uranium is: [Rn]5f36d17s2.
The electron Configuration [Ra] 7s2 5f8 is Not Valid because Ra is basically [Rn] 7s2. However, you have Ra 7s2 5f8. You can never repeat and electron configuration piece twice, or at all.
[Rn] 7s2 is the noble gas notation for radium. A link is provided to the Wikipedia article on radium.
[Rn]7s2
Mendelevium (Md)
[Rn] 5f6 7s2.
Ra, radium
[Rn]5f14 7s2 7p1
[Rn] 5f6 7s2
[Rn] 5f9 7s2
[Rn] 7s2 5f1
The electron configuration of uranium is: [Rn]5f36d17s2.
[Rn] 5f14 7s2