NCERT Exercise 2.22 - Structure of Atom
Question: Identify isoelectronic species among Na+, K+, Mg2+, Ca2+, S2- and Ar.
Answer: Na+, Mg2+ and Ca2+ are isoelectronic; Ar, S2- and K+ are isoelectronic.
Full step-by-step NCERT solution with diagrams on Something by Zero.