Question

Which of the following ions is not isoelectronic with $O^{-2}$?
(A)$N^{-3}$
(B)$N{a}^{+}$
(C)$F^{-}$
(D)$T{i}^{+3}$

Answer 1

Hint: Elements or ions having equal number of electrons are called isoelectronic species. They also have the same electronic configuration. To find the isoelectronic pairs, we have to just add the number of electrons of each atom present in the species and also add the charge of the species. If the number of electrons are equal in both the species, then they can be called isoelectronic pairs.

Complete answer:
Isoelectronic species are the ions of different elements which consist of the same number of electrons but are different from one another in magnitude of the nuclear charge. These species have the same number of valence electrons and they have the same structure i.e. the number of atoms and the connectivity of atoms but differ in some of the elements involved. The species that have the same shape and same hybridization are called isostructural species and these species have the same number of valence electrons. To identify isostructural species, we need to check for the pairs having the same shape and hybridization. Oxygen anion has $10$ electrons. $N{a}^{+}$ has $10$ electrons and $F^{-}$ has $10$ electrons. $Ti$ has an atomic number $22$ which is not isoelectronic with the oxygen anion. So, $T{i}^{+3}$ is not isoelectronic with $O^{-2}$.

Therefore, option D is correct.

Note:
The term isoelectronic is used to refer to two atoms, ions or even molecules that have the same electronic configuration as well as the same number of valence electrons. Isoelectronic means equal charge. Generally, isoelectronic species display similar chemical properties.