The ionic radii of K⁺, Na⁺, Al³⁺ and Mg²⁺ are in the order:

Which one of the following statements for D.I. Mendeleeff, is incorrect?

The first ionization energy of magnesium is smaller as compared to that of elements X and Y, but higher than that of Z. The elements X, Y and Z, respectively, are :

The ionic radius of Na⁺ ions is 1.02 $$\mathop A\limits^o $$. The ionic radii (in $$\mathop A\limits^o $$) of Mg²⁺ and Al³⁺, respectively, are