Question

The ions $O^{2–},F^{–},N{a}^{+},M{g}^{2+}$ and $A{l}^{3+}$ are isoelectronic. Their ionic radii show:

• A. An increase from $O^{2–}$ to $F^{–}$ and then decrease from $N{a}^{+}$ to $A{l}^{3+}$
• B. A significant decrease from $O^{2–}$ to $A{l}^{3+}$
• C. A significant increase from $O^{2–}$ to $A{l}^{3+}$
• D. A decrease from $O^{2–}$ to $F^{–}$ and then increase from $N{a}^{+}$ to$A{l}^{3+}$

Answer 1

The correct option is B A significant decrease from $O^{2–}$ to $A{l}^{3+}$

Amongst isoelectronic ions, ionic radii of anions is more than that of cations. Further size of the anion increases with increase in –ve charge and size of cation decreases with increase in +ve charge. Hence, correct order is $O^{2–}>F^{–}>N{a}^{+}>M{g}^{2+}>A{l}^{3+}$.