Here's why:
* Electron Configuration: Gadolinium's electron configuration is [Xe] 4f7 5d1 6s2.
* Valence Electrons: Valence electrons are the electrons in the outermost energy level. In gadolinium's case, these are the electrons in the 5d and 6s orbitals.
* Total: There's one electron in the 5d orbital and two electrons in the 6s orbital, totaling 8 valence electrons.
