Consider the following isoelectronic species: . What is the exact number of species from this list t — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

For isoelectronic species (all have 10 electrons here), size is inversely proportional to atomic number ($Z$). The order of sizes is $O^{2-} (Z=8) > F^- (Z=9) > Na^+ (Z=11) > Mg^{2+} (Z=12) > Al^{3+} (Z=13)$. The species smaller than $F^-$ are $Na^+$, $Mg^{2+}$, and $Al^{3+}$, totaling 3 species.