Question

which of the following are iso electronic species having same number of electron ​
Na+,K+, Mg2+, Ca2+ ,S2- Ar

Answer 1

so there are two isoelectric species

first is of 10 electrons which are Mg2+ and Na+ (these ions contain same number of electrons. {10 electrons})

second is of 18 electron Which are K+, Ca2+, S2- and Ar (these ions contain same number of electrons. {18 electrons})