2A17a.

[Carly Yoon]

Are electrons in the outermost d-orbital always considered valence electrons?
For example, for 2A17a., why does Mn4+ have 3 valence electrons? I understand that there are 3 electrons left in the 3d orbital - but isn't the 3d orbital part of the 3 energy level/shell...?

[Lily Zello 3I]

I'm not totally sure about the answer to the first part of your question, but I think that d-orbital electrons are only considered valence electrons when the subshell is not fully filled. So, for Mn, you would count d-orbital electrons as valence electrons, giving it a total of 7 valence electrons. After Mn4+ loses its first 2 electrons from 4s, it must lose the next two from 3d since the 3 energy level/shell is the next highest energy level of the atom.