Write the core notation of

Sr 2+

is it
[Ar] 3d10 4s2 4p6
or
[Ar]4s2 3d10 4p4 5s2
since you subtract from p before s before d

thanks in advance.

3 answers

Neither.
http://www.webelements.com/strontium/atoms.html
Hmm.. if it's just Sr, then the core notation would be [Kr] 5s2, then you minus 2 electrons to [Kr]5s0?
That's right.
Sr^+2 = [Kr]. I don't suppose its necessary to put 5so but I don't think it's wrong to do it either.