Question

Which of the following is isoelectronic with neon?
A.${\mathrm{O}}^{2-}$
B.$\mathrm{F}$
C.$\mathrm{M}\mathrm{g}$
D. $\mathrm{N}\mathrm{a}$

Answer 1

Hint:We know that isoelectronic species are those species which have the same number of electrons and same structure.

Complete step by step answer:
To identify the species which are isoelectronic with neon, we first have to count the electrons of neon. Neon is an inert gas present in group 18 of the periodic table. The atomic number of neon is 10. So, electrons present in neon are 10. So, to be isoelectronic with neon, an element must have ten electrons.

In ${\mathrm{O}}^{2-}$, the -2 charge indicates that two electrons are gained by an oxygen atom to complete its octet. The atomic number of oxygen is eight,that means, the number of electrons in an oxygen atom is eight. In ${\mathrm{O}}^{2-}$, due to gaining of two electrons the number of electrons is ten. So, ${\mathrm{O}}^{2-}$is isoelectronic with neon. Hence, option A is correct.

The atomic number of fluorine ($\mathrm{F}$) is nine, that means, the number of electrons in fluorine is nine. So, $\mathrm{F}$is not isoelectronic with neon. So, option B is incorrect.

Magnesium $\left(\mathrm{M}\mathrm{g}\right)$is the element whose atomic number is 12. So, the number of electrons in magnesium is 12. So, Magnesium is not isoelectronic with neon. So, option C is incorrect.

Sodium $\left(\mathrm{N}\mathrm{a}\right)$is the element whose atomic number is 11. So, the number of electrons in magnesium is 11. So, sodium is not isoelectronic with neon. So, option D is incorrect.

Note:
Neon has 10 electrons and the elements which are electronic with neon also have 10 electrons. Some other elements except ${\mathrm{O}}^{2-}$which are isoelectronic with neon are sodium ion $\left(\mathrm{N}{\mathrm{a}}^{+}\right)$, fluoride ion $\left({\mathrm{F}}^{-}\right)$etc. Sodium ion and fluoride ion both have ten electrons.