Why does sodium have a higher second ionisation energy than magnesium?
- AThe attraction between the nucleus and the outer electron is greater in $\text{Na}^+$ than in $\text{Mg}^+.$
- BThe nuclear charge of $\text{Na}^+$ is greater than that of $\text{Mg}^+.$
- CThe outer electron of $\text{Na}^+$ is more shielded than the outer electron of $\text{Mg}^+.$
- DThe outer electron of Na is in the same orbital as the outer electron of Mg.