Question

what are the four quantum numbers of the last electron of As

this is what i have
n=4
l=1
ms= 1/2

i don't know how to calculate ml. I know it's either: -1,0,1

Answer 1

Here is a site that gives the electron configuration showing
3d10 4s2 4p3.
Thus for the last electron, that will be the one that is 4p and I usually fill the -1, then 0, then +1 for m_l. You are correct on n, m_s and and l.

Answer 2

so it will be 1 as the last electron comes on that one correct?
umm and i don't see the link you posted :S

Answer 3

You didn't see it because I didn't post it. Sorry about that.
http://www.webelements.com/arsenic/atoms.html
Yes, 1 for m_l is what I would do.