When a sample of Mg(s) reacts completely with O(g), the Mg(s) loses 5 moles of electrons. How many moles of electrons are gained by the O2(g)?
1.0 mol
2.5 mol
5.0 mol
4
10.0 mol​

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!