The ns and (n-1)d subshells are so close in energy that
Once d elecrons are added, the (n-1)d subshell becomes sligtly
lower in energy than the ns subshell.
As a result, the ns electrons are at higher energy and
Are always removed before (n-1)d electrons when transition metals
form cation.
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여기서만 20분째 고민중인데 도와주실분 계신가요?