Explain why for sodium the second ionization potential is so much larger than the first, whereas for magnesium the magnitude of the difference between the first and second ionization potential is much less?

Explanation

Which has completely filled octet (higher stability) but `Na^(+) -1e to Na^(+2)` will result in to less stable electronic configuration thus higher second I.P. than expected. For, `Mg^(+1) -1e to Mg^(+2)" as "Mg^(+1)` has less stable electronic configura- tion compared to `Mg^(+2)` hence, 2nd I.P. of Mg is less than expected.