What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions.
(i) F^-  (ii) Ar    (iii) Mg²⁺   (iv) Rb⁺ 

Consider the following species : N^3-, O^2-, F^-, Na⁺, Mg²⁺ and Al³⁺

(a) What is common in them?

(b) Arrange them in the order of increasing ionic radii. 

Give the formula of a species which will be isoelectronic with the following atoms or ions:
(i) Na²⁺ 
(ii) Cl^- 
(iii) Ca²⁺ 
(iv) Rb⁺.

Which of the following species will have the largest and the smallest size?
Mg, Mg²⁺, Al, Al³⁺.

119.

Arrange the following ions in order of increasing size:
Be²⁺, Cl^-, S^2-, Na⁺, Mg²⁺, Br^-.

In each of the following pairs,  which species has a larger size? Explain.
(i) K or K⁺ 
(ii) Br or Br^- 
(iii) O^2- or F^- 
(iv) Li⁺ or Na⁺ 
(v) P or As
(vi) Na⁺ or Mg²⁺