Which of the following concerning second ionization energies is true?

A. That of Al is lower than that of Mg because Mg wants to lose the second electron, thus the energy change is greater.
B. That of Al is higher than that of Mg because the electrons are taken from the same energy level, but the Al atom has one more proton.
C. That of Al is lower than that of Mg because the second electron taken from Al is in a p orbital, thus it is easier to take.
D. That of Al is higher than that of Mg because Mg wants to lose the second electron, so it is easier to take the second electron away.
E. The second ionization energies are equal for Al and Mg.

The fact is that the both elements belong to different groups in the periodic table. Mg is in group 12 while Al is in group 13. The outer most electron configuration for Mg2+=[Ne]3s0

Al+= [Ne]3s13p0

It is evident that in Al+, the second electron is to be removed from a filled 3s subshell which is energetically unfavourable. Unlike In Mg2+ where the two electrons are removed. There is always a tendency towards a quick loss of all the valence electrons in the valence shell. It will be more difficult to remove an electron from a filled shell.