What is the total number of electrons in a #Mg^(2+)# ion?
The easiest way to do this is to simply look at the periodic table, find the atomic number of magnesium, and subtract 2 from it. The reason this works is that the atomic number tells you how many protons an element has. If we want the element to be neutral, then by definition it will have the same number of electrons.
Why subtract two though? Well, that's just because you're asking about the
Another way you could do this would be to write out the electron configuration of Mg. This would be:
Recall that the superscripts tell us how many electrons occupy each orbital, so adding all the superscripts will tell us how many electrons we have. So if you add them up, then subtract two to account for the 2+ ionic charge, you will get the right number of electrons.
In either case, you will end up with
Hope that helped :)