atomic and ionic radii

Question

Which of the following ions has the largest ionic radius?

RankGuru · Accepted Answer

All the given species ($O^{2-}, F^-, Na^+, Mg^{2+}$) are **isoelectronic**, meaning they all have 10 electrons.
- For isoelectronic species, the ionic radius is inversely proportional to the **atomic number ($Z$)** (nuclear charge).
- **$O^{2-}$ ($Z=8$):** 8 protons pull 10 electrons (Weakest pull $	o$ Largest size)
- **$F^-$ ($Z=9$):** 9 protons pull 10 electrons
- **$Na^+$ ($Z=11$):** 11 protons pull 10 electrons
- **$Mg^{2+}$ ($Z=12$):** 12 protons pull 10 electrons (Strongest pull $	o$ Smallest size)
Trend: $O^{2-} > F^- > Na^+ > Mg^{2+}$.

Rank Guru

atomic and ionic radii

Select the correct option: