Question

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.

Answer 1

Neither.
http://www.webelements.com/strontium/atoms.html

Answer 2

Hmm.. if it's just Sr, then the core notation would be [Kr] 5s2, then you minus 2 electrons to [Kr]5s0?

Answer 3

That's right.
Sr^+2 = [Kr]. I don't suppose its necessary to put 5s^o but I don't think it's wrong to do it either.