Electron Configuration of Platinum

1. τheory

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1. The problem statement, all variables and given/known data
Why is the electron configuration of neutral Platinum:

$Pt = [Xe]4f ^{14} 5d ^{9} 6s ^{1}$

and not?:

$Pt = [Xe]4f ^{14} 5d ^{10} 6s ^{0}$

I thought that if the two electrons from the 6s sub-shell were to move to the 5d sub-shell, then 5d sub-shell would be fully paired, hence stability? However, this is not the case as the actual configuration calls for only one electron to be moved from the 6s sub-shell, rather than two. Can someone explain to me why this is the case?