Question

Nature of ${{O}_{2}}$ is
A. Paramagnetic
B. Diamagnetic
C. Both A and B
D. None of these

Answer 1

Hint: Magnetic character of molecules most commonly determined by the number of unpaired electrons present in the molecule.

Complete answer:
Paramagnetism and diamagnetism are the terms used to refer to the magnetic behaviour of a molecule to fully stop the magnetic behaviour of molecules depending upon the pairing of electrons in orbitals.
When two electrons occupy an orbital, they necessarily have different spin Quantum numbers. When the electrons are paired in any orbital their net Spin is zero and electrons are called diamagnetic electrons. Molecules or atoms which have all period electrons are called diamagnetic. If the net spin of an orbital is non-zero it means that the orbital has only one electron which must be unpaired. Such unpaired electrons are called paramagnetic electrons and molecules are called paramagnetic molecules or atoms.
Diamagnetic atoms show repulsion towards the magnetic field which means that they move away from the external magnetic field and paramagnetic atoms or molecules show attraction towards the magnetic field, that is they align themselves towards the external magnetic field.
${{O}_{2}}$ molecule is paramagnetic in nature. The paramagnetic nature of ${{O}_{2}}$ is determined by Molecular orbital theory. The molecular orbital diagram is shown below. This theory proves that an oxygen molecule has two unpaired electrons and is paramagnetic in nature.
If Lewis structure of oxygen molecule is drawn it demonstrates that all the electrons in oxygen are paired which is a misleading statement and proves that oxygen is a diamagnetic molecule. So Molecular orbital theory must be used.

The correct answer is (A).

Note: The paramagnetic molecules or atoms can also have diamagnetic or paired electrons but they must have at least one unpaired electron to be paramagnetic.