1. **Problem statement:** Arrange the ions F⁻, Na⁺, N³⁻, and Mg²⁺ in order of increasing size and explain the reasoning. 2. **Key concept:** Ionic size depends on the number of electrons and the effective nuclear charge. More positive charge on the ion pulls electrons closer, reducing size. More negative charge adds electrons, increasing size. 3. **Ions and their charges:** - F⁻ (fluoride ion): 9 protons, 10 electrons - Na⁺ (sodium ion): 11 protons, 10 electrons - N³⁻ (nitride ion): 7 protons, 10 electrons - Mg²⁺ (magnesium ion): 12 protons, 10 electrons 4. **Analysis:** All ions have 10 electrons (isoelectronic), so size differences arise from nuclear charge. 5. **Effective nuclear charge order:** - N³⁻: 7 protons - F⁻: 9 protons - Na⁺: 11 protons - Mg²⁺: 12 protons 6. **Size order:** More protons mean stronger attraction and smaller size. Therefore, size increases as nuclear charge decreases: $$\text{Mg}^{2+} < \text{Na}^+ < \text{F}^- < \text{N}^{3-}$$ 7. **Final answer:** The order of increasing ionic size is $$\boxed{\text{Mg}^{2+} < \text{Na}^+ < \text{F}^- < \text{N}^{3-}}$$ This is because ions with higher positive charge have smaller radii due to stronger attraction of electrons by the nucleus, while ions with more negative charge have larger radii due to increased electron-electron repulsion and lower effective nuclear charge per electron.