Question

The isoelectronic set of ions is:
A. ${{N}^{3-}},L{{i}^{+}},M{{g}^{2+}}\text{ and }{{\text{O}}^{2-}}$
B. $L{{i}^{+}}\text{,}N{{a}^{+}}\text{,}{{\text{O}}^{2-}}\text{ and }{{F}^{-}}$
C. ${{F}^{-}}\text{,}L{{i}^{+}}\text{,}N{{a}^{+}}\text{ and }M{{g}^{2+}}$
D. ${{N}^{3-}},{{\text{O}}^{2-}},{{F}^{-}}\text{ and }N{{a}^{+}}$

Answer 1

. The isoelectronic species are those species which have the same number of electrons in them no matter what their atomic number is or what their group number or period number is.

Complete step by step answer:
-There are 7 periods and 18 groups in periodic tables where atoms are arranged in the increasing order of their atomic number because the atomic number gives us the number of electrons of the atom. Electrons only decide the chemical properties of an atom as they are loosely held by the atom.

-We know that atoms can either gain/lose electrons to achieve the electronic configuration state of noble gases or they can share electrons. Ionic bonds are created by gaining/losing electrons and covalent bonds by sharing electrons.
-Noble gases are the most stable elements of the periodic table because they have complete octets. It means that their shells are complete. So they do not need to react to gain stability. All other elements react to achieve their electronic configuration state.

-All the given options are ions and so they can achieve the noble gas configuration by losing or gaining electrons. Let us study all the given ions 1 by 1 to see if they reach noble gas configuration or not.
-We need to find the number of electrons present in those ions. For that we need to find the electrons present in the respective atom first and then the ion. Anions gain electrons and cations lose electrons.
-N has the atomic number of 7 and it gains 3 electrons to attain the configuration of noble gas Ne. So total electrons in the ion will be 7 + 3 = 10. O, with atomic number 8, will gain 2 electrons to do so. F, with atomic number 9, will gain 1 electron like N and O.

-Lithium, sodium and magnesium are metals and they will lose electrons to reach the configuration of their nearest noble gas. Li has atomic number 3 and so it loses 1 electron to attain the configuration of He with 2 electrons in total.
-Sodium and magnesium have atomic numbers 11 and 12 respectively and they lose 1 and 2 electrons respectively to attain the configuration of Ne. The electrons in sodium ion will be 11 - 1 = 10 and in magnesium ion will be 12 - 2 = 10.

-Thus we see that the ions formed by sodium, magnesium, nitrogen, oxygen and fluorine have the same number of electrons in them which is equal to 10 and is the number of electrons present in Ne gas which is a noble gas.
So, the correct answer is “Option D”.

Note: The periodic table is made in such a form that it can show the variations of several properties of the atoms both along the period and down the group. This is the reason why it is arranged based on the atomic number and not atomic mass.