Which would have a greater value for the second ionisation energy: magnesium or aluminium?
Mg+ has an electronic configuration of 1s22s22s63s1, Al+ has an electronic configuration of 1s22s22s63s2.
Shielding in both Mg+ and Al+ is the same.
Proton number increases.
Effective nuclear charge on the outermost electrons increases for Al+, making the atom smaller.
The Ionisation Energy increases for Al+