Question

Which of the following species is isoelectronic with $CO$?
a.) $HF$
b.) ${{N}_{2}}$
c.) $N_{2}^{+}$
d.) ${{O}_{2}}^{-}$

Answer 1

Hint: If the numbers of electrons in species are equal then they are isoelectronic.
When the number of electrons is the same in different species that can be atoms, molecules or ions then they are known as isoelectronic species.

Complete answer:
Now, we will calculate the number of electrons in ions or molecules given in the above options: No. of electrons in carbon monoxide is calculated by adding the number of electrons in carbon and number of electrons in oxygen.
Number of electrons in carbon=6
Number of electrons in oxygen=8
Number of electrons in $CO$ : 6+8=14
Number of electrons in hydrogen fluoride is calculate by adding the number of electrons in hydrogen and number of electrons in fluoride
Number of electrons in hydrogen=6
Number of electrons in fluorine=8
Number of electrons $HF$:1+9=10
Number of electrons in nitrogen molecule is calculated by adding the number of electron in nitrogen atoms
Number of electrons in nitrogen=7
Number of electrons in ${{N}_{2}}$ : 7+7=14
Number of electrons in $N_{2}^{+}$ is calculated by adding the number of electrons in nitrogen atoms and then subtracting 1 electron for overall positive charge.

Number of electrons in $N_{2}^{+}$​ : 7+7-1=13

Number of electrons in ${{O}_{2}}^{-}$ is calculated by calculating the total number of electrons present in oxygen molecule and then subtracting one electron for overall negative charge present on ${{O}_{2}}^{-}$ molecule.

Number of electrons in ${{O}_{2}}^{-}$ : 8+8+1=17
Since carbon monoxide and nitrogen molecules have the same number of electrons therefore, $CO$ and ​${{N}_{2}}$are isoelectronic.

The correct option is B.

Note: When the number of electrons is the same in different species that can be atoms, molecules or ions then they are known as isoelectronic species.