Which one of the following pairs do not have the same electronic structure?

Answer:

14) A

A – Correct
Mg has 2 electrons on its outer shell. Each of these electrons will go to each of the Cl atoms. These chloride atoms will have the same electronic structure as an Ar atom. However, the Mg atom would have the electronic structure of a Ne atom. Hence, this is the answer.

B – Wrong
Carbon has 4 electrons on its outer shell. It forms a triple bond with O. Both C and O would have eight electron on their outer shells.
These N atoms form a triple bond between each other. Both atoms would have eight electrons in their outer shell.
Hence this is not the answer.

C – Wrong
C covalently bonds with 4 H atoms. C would have eight electrons in its outer shell and each of the H atoms would have 2 electrons in their outer shell.
The N covalently bonds with 3 H atoms and forms a co-ordinate bond with a fourth H+ ion. The Nitrogen will have eight electrons in its outer shell and each of the H atoms would have 2 electrons in their outer shell.

D – Wrong
N covalently bonds with 3 O atoms. It forms a single bond with 2 O atoms and a double bond with the third O atom. All atoms would have eight electrons in their outer shells.
C covalently bonds with 3 O atoms. It forms a single bond with 2 O atoms and a double bond with the third O atom. All atoms would have eight electrons in their outer shells.

E – Wrong
Na has 1 electron in its outer shell. This electron will go to the F atom. Both Na and F atoms will have the same electronic structure as a Ne atom.