Write the electron configuration in order of increasing energy

Question

Co^2+ (Cobalt 2+) 

 

This is a mastering chem question which i could not get right after several tries

 

my tries are 

 

[Ar]3d^7

 

[Ar]4s^03d^7

 

[Ar]4s^23d^5

Answer 1

Is the question asking specifically for the electronic configuration of Co2+ or does it want the condensed electronic configuration? These are two types of electronic configuration and in the 'simple' electronic configuration you cannot use the noble gas configuration as you can use in the condensed electronic configuration. Now the correct answer using condensed electronic configuration should be [Ar]3d7 since the 4s electrons are lost first but if you use 'simple' electronic configuration then the answer is 1s2, 2s2, 2p6, 3s2, 3p6,3d7