What do you understand by isoelectronic species ? Name the , species isoelectronic with each of the following.
i) `F^(-1)` ii) Ar iii) `Mg^(2+)` iv) `Rb^(+)`

Explanation

The neutral atoms or ions of different elements having same number of electrons are called isoelectronic species :
i) `F^(-)`
Atomic number of F=9
So, number of electrons in F = 9
and number of electrons in `F^(-1)=10`.
The other species having 10 electrons are `Ne, Na^(+), Mg^(2+)` and these species are isoelectronic to `F^(-)`
Ar
Atomic number of Ar=18
So, number of electrons in `F^(-)=10`
The other species having 18 electrons are `Cl^(-),K^(+), Ca^(2+)` are isoelectronic to Ar.
`Mg^(2+)`
Atomic number of Mg=12
So, the number of electrons in Mg=12.
The other species having 10 electrons are `Ne,Na^(+),F^(-)` are isoelectonic to `Mg^(2+)`.
`Rb^(+)`
Atomic number of Rb =37
The number of electrons in Rb=37
So, the number of electrons in `Rb^(+)=36`.
The other species having 36 electrons are `Kr,Br^(-),Sr^(2+)` are isoelectronic with `Rb^(+)`.