Question

Arrange Na⁺ , Mg²⁺ and Al³⁺ in the increasing order of ionic radii. Give reason.

Answer 1

Na⁺ , Mg²⁺ and Al³⁺ are iso electronic cations.

Ions	Na+	Mg2+	Al3+
Number of electrons	10	10	10
Number of nuclear charge	11	12	13

The cation with the greater positive charge will have a smaller radius because of the greater attraction of the electrons to the nucleus. 

Hence the increasing order of ionic radii is, 

r_Na⁺ > r_Mg²⁺ > r_Al³⁺