Nitrosonium ion $(N{O^ + })$ is isoelectronic with:
A) Carbon dioxide
B) Carbon monoxide
C) Nitrogen dioxide
D) Nitric oxide

Hint: The term isoelectronic means having the same number of electrons or having the same electronic configuration. One needs to calculate the number of electrons in the nitrosonium ion and relate them with the options given one by one and find out the correct choice.

Complete step by step answer:
1) First of all we will calculate the number of electrons that are present in the nitrosonium ion. The nitrosonium ion molecular formula is $(N{O^ + })$ and the number of electrons present in it follows,
$N{O^ + } = 7 + 8 - 1 = 14$
Where nitrogen has seven electrons, oxygen has eight electrons and due to the one positive charge, there will be the subtraction of one electron.
2) Now let's see for the isoelectronic structures by analyzing each option and calculating its electrons one by one, the Carbon dioxide has molecular formula as $C{O_2}$ and it has $6 + 8 + 8 = 22$ electrons which are not equal to the electrons present in the nitrosonium ion hence this option is an incorrect choice.
3) The Carbon monoxide has the molecular formula as ${\text{CO}}$ and it has the $6 + 8 = 14$ electrons which are equal to the number of electrons present in the nitrosonium ion hence this option is a correct choice of answer.
4) The Nitrogen dioxide has the molecular formula as $N{O_2}$ and it has $7 + 8 + 8 = 23$ electrons that are not equal to the number of electrons in the nitrosonium ion hence this option is an incorrect choice.
5) The Nitric oxide has the molecular formulas as ${\text{NO}}$ and it has the $7 + 8 = 15$ electrons which are not equal to the number of electrons in the nitrosonium ion hence this option is an incorrect choice.
6) Therefore, after analyzing all the options Nitrosonium ion $(N{O^ + })$ is isoelectronic with Carbon monoxide

Therefore, the correct option is B.

Note:
While counting the number of electrons when there is a positive charge on the atom or a molecule one needs to subtract the number of positive charge from the total electrons and when there is a negative charge on the atom or molecule on the need to add the negative number to total electron count.