The species Ar,K⁺ and Ca²⁺ contain the same number of electrons.In which order do their radii increase

Options

(a) Ca²⁺ < Ar < K⁺
(b) Ca²⁺ < K⁺ < Ar
(c) K⁺ < Ar < Ca²⁺
(d) Ar < K⁺ < Ca²⁺

Correct Answer:

Ca²⁺ < K⁺ < Ar

Explanation:

In isoelectronic species the radius decrease with increase in nuclear charge hence increasing order of radius is Ca⁺² < K⁺< Ar