Question

The species Ar, K⁺ and Ca²⁺ contain the same number of
electrons. In which order do their radii increase ?
(a) Ca²⁺ < Ar < K⁺
(b) Ca²⁺ < K⁺ < Ar
(c) K⁺ < Ar < Ca²⁺
(d) Ar < K⁺ < Ca²⁺