Answer : The correct answer will be A =3 and B =2 as the electron configuration of Mg will be as [tex] [Ne] 3s^{2}[/tex] where A is 3 and B is 2.
Explanation :
Magnesium has atomic number as 12. The complete electron configuration will be as [tex] 1s^{2}2s^{2}2p^{6}3s^{2}[/tex].
which can be abbreviated as[tex][Ne] 3s^{2}[/tex] as the electron configuration resembles to that of neon element.
In the outermost shell the electron in 3 s orbital is only 2. So, therefore 3 is the orbital of S and there are 2 electrons in it.
