Materials Science and Engineering

Magnesium has a full 3S (highest energy shell). Why is it still a metal and conducting?

a. 3s is not full all the time and one electron

b. 3s and 3p form an energy band overlap that is partially unfilled

c. two of the electrons in 2P form a higher level 3p electronic sub-shell which is partially unfilled

d. None of the above

I am debating between b. and d. The concept for b. is correct, but Magnesium spdf structure is 1s2 2s2 2p6 3s2, without a 3p sub-shell, so I would say that the 2p and 3s shells are the ones that overlap and form a partially unfilled energy band.

Which is correct: b. or d.?