The electron configuration of protactinium (Pa) is [Rn] 5f^2 6d^1 7s^2.
To break it down:
- [Rn] represents the electron configuration of the previous noble gas, radon (Rn), which is [Xe] 6s^2 4f^14 5d^10.
- 5f^2 indicates that there are two electrons in the 5f orbital.
- 6d^1 indicates that there is one electron in the 6d orbital.
- 7s^2 indicates that there are two electrons in the 7s orbital.
So, the electron configuration of protactinium is obtained by adding the electron configuration of radon and then filling in the additional electrons specific to protactinium.