Why is the second ionisation energy of Na much greater than the second ionisation energy of Mg?

The second ionization energy of sodium (Na) is much greater than that of magnesium (Mg) because of the difference in their electronic configurations and the stability of the resulting ions. When Na loses its first electron, it achieves a stable noble gas configuration (Neon), making the removal of a second electron from the positively charged Na⁺ ion much more difficult. In contrast, when magnesium loses its first electron, it still has a relatively stable electron configuration and retains two valence electrons, making the second ionization less energetically demanding. Thus, the increased stability of Na⁺ compared to Mg⁺ contributes to the significantly higher second ionization energy for Na.