Question

In which of the following molecule, cation is not isoelectronic with anion?

• A. Potassium fluoride
• B. Aluminium fluoride
• C. Sodium fluoride
• D. Potassium chloride

Answer 1

The correct option is A Potassium fluoride

Isoelectronic species are those which contain the same number of electrons.
If cation and anion do not contain the same electrons, they are not isoelectronic.

Cation is not isoelectronic with anion in $KF$, because the cation $K^{+}$ contains 18 electrons whereas, the anion $F^{-}$ contains 10 electrons. Remaining all other molecules contain the same number of electrons in the cation as well as the anion.

In aluminium fluoride, $A{l}^{3+}$ has 10 electrons and $F^{-}$ has 10 electrons.

In sodium fluoride, $N{a}^{+}$ has 10 electrons and $F^{-}$ has 10 electrons.

In potassium chloride, $K^{+}$ has 18 electrons and $C{l}^{-}$ has 18 electrons.