Question

The ions \( \text{O}^{2-} \), \( \text{F}^- \), \( \text{Na}^+ \), \( \text{Mg}^{2+} \) and \( \text{Al}^{3+} \) are isoelectronic. Their ionic radii show:

• A. A decrease from \( \text{O}^{2-} \) to \( \text{F}^- \) and then increase from \( \text{Na}^+ \) to \( \text{Al}^{3+} \)
• B. A significant increase from \( \text{O}^{2-} \) to \( \text{F}^- \)
• C. A significant decrease from \( \text{O}^{2-} \) to \( \text{Al}^{3+} \)
• D. An increase from \( \text{O}^{2-} \) to \( \text{F}^- \) and then decrease from \( \text{Na}^+ \) to \( \text{Al}^{3+} \)

Hint:

For isoelectronic ions, the ionic radius decreases with increasing nuclear charge due to stronger attraction of electrons by the nucleus.

Answer 1

The Correct Option is C

Step 1: Understand the trend in ionic radii.
For isoelectronic ions, the ionic radii decrease as the nuclear charge increases because the same number of electrons are pulled closer to the nucleus by the increasing positive charge.
Step 2: Conclusion.
The ionic radius decreases significantly from \( \text{O}^{2-} \) to \( \text{Al}^{3+} \) due to the increasing nuclear charge. Final Answer: \[ \boxed{\text{A significant decrease from } \text{O}^{2-} \text{ to } \text{Al}^{3+}} \]