Valence shell of transition metals definition is what?

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TL;DR Summary

Four cases what's valence electrons?

Case one: ns is half-filled and (n-1)d is less than full.
Is valence 1+number of electrons in (n-1)d or number of electrons in (n-1)d or 1?

Case two: ns is fully filled and (n-1)d is less than full
Is valence 2 or 2+ number of electrons in (n-1)d or number of electrons in (n-1)d?

Case three, ns is fully filled, and (n-1)d is full
is valence 12 or 2 or 10?

Case four: ns is half-filled, and (n-1)d is full.
is valence 1 or 1+10 or 10?

 

[Borek]

https://en.wikipedia.org/wiki/Valence_electron#Electron_configuration

Valence shells/electrons are one of these simplified concepts that work nicely for basics, but become problematic when you dig into details and more complicated cases.