Question

In which of the following pairs, the ions are iso-electronic?
This question has multiple answers.
A) $N{a^ + },M{g^{2 + }}$
B) $A{l^{3 + }},{O^ - }$
C) $N{a^ + },{O^{2 - }}$
D) $N{a^{2 + }},C{l^ - }$

Answer 1

We have to know that iso-electronic species/ions/atoms are the species which have same number of electrons but different magnitude of nuclear charges & belongs to different atoms or ions and they are different in their physical and chemical properties

Complete answer:
We have to know that isoelectronic pairs are those pairs of atoms, ions or molecules that have the same number of electrons in them. For finding the isoelectronic pairs, we can just add the number of electrons of each atom in the species and also the charge of the species (if present).
We will look for all the options one by one:
Option A) this option is correct as the number of electrons for both sodium and magnesium are the same i.e. $10$. Thus they are isoelectronic pairs.
Option B) this option is incorrect as the number of electrons is not the same. For aluminum it's $10$ while for oxygen it's $9$, thus they are not isoelectronic pairs.
Option C) this option is correct as the number of electrons for both sodium and oxygen are the same i.e. $10$. Thus they are isoelectronic pairs.
Option D) this option is incorrect as the number of electrons for both sodium and chlorine is not the same. Thus they are not isoelectronic pairs.

Option A is the correct answer.

Note:
We need to know that if two or more species have the same electronic configuration they are said to be isoelectronic. Note that isoelectronic species tend to have very similar chemical properties. For finding the isoelectronic pairs, we can just add the number of electrons of each atom in the species and also the charge of the species (if present).