6th edition 3.9 and 3.11

[katherinemurk 2B]

Can someone please explain the answers to these two questions. I do not understand them at all. Thank you in advance!

[Tam To 1B]

These questions are basically asking which metal ions with a 2+ charge would have the electron configuration given? The 2+ charge means that 2 electrons were taken away to get the positive charge.
For instance, 3.9a) [Ar]3d^7
Add back 2 electrons to get [Ar]3d^7, 4s^2. (Remember 4s fills up before 3d but 4s is on the outer shell so that's why electrons are taken off from that shell)
This electron configuration would be for Cobalt, so the ion with electron configuration [Ar]3d^7 is Co2+.