Question

The ions O^2- , F^- , Na⁺, Mg²⁺ and Al³⁺ are isoelectronic. Their ionic radii show 

(a) a significant increase from O^2- to Al³⁺ 

(b) a significant decrease from O^2- to Al³⁺ 

(c) an increase from O^2- to F^- and then decrease from Na⁺ to Al³⁺ 

(d) a decrease from O^2- to F^- and then increase from Na⁺ to Al³⁺

Answer 1

The correct option is : (b) a significant decrease from O^2- to Al³⁺ 

Explanation:

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^- > Na⁺ > Mg²⁺ > Al³⁺