Explanation:

Molecular Orbital Theory:
The molecular orbital theory (MO theory) is a model used to explain the electronic structure of molecules. According to this theory, electrons in a molecule are not assigned to individual bonds between atoms but rather exist in molecular orbitals that are spread over the entire molecule. These molecular orbitals are formed by the combination of atomic orbitals from the participating atoms.

Paramagnetism:
Paramagnetism refers to the property of a substance to be attracted to an external magnetic field. It occurs when there are unpaired electrons in the molecular orbitals of a substance.

Oxygen Molecule:
The oxygen molecule (O2) consists of two oxygen atoms, each with six valence electrons. In the ground state, these electrons occupy the 2s and 2p orbitals of the oxygen atoms.

Molecular Orbital Diagram:
The molecular orbital diagram for O2 can be constructed by combining the atomic orbitals of the oxygen atoms. The 2s orbitals of the oxygen atoms combine to form a sigma (σ) bonding orbital and a sigma* (σ*) antibonding orbital. Similarly, the 2p orbitals combine to form two pi (π) bonding orbitals and two pi* (π*) antibonding orbitals.

Electronic Configuration:
In the ground state of O2, the electrons fill the molecular orbitals according to Hund's rule and the aufbau principle. The sigma bonding orbital is filled with two electrons of opposite spin, followed by the two pi bonding orbitals, each filled with two electrons. This gives a total of six electrons in the bonding orbitals and two electrons in the antibonding orbitals.

Paramagnetic Nature:
The paramagnetic nature of O2 can be explained by the presence of two unpaired electrons in the pi* antibonding orbitals. These unpaired electrons have parallel spins, which make the oxygen molecule attracted to an external magnetic field. Therefore, O2 is considered paramagnetic.

Conclusion:
In conclusion, the paramagnetic nature of the oxygen molecule can be explained by the molecular orbital theory. The presence of two unpaired electrons in the pi* antibonding orbitals leads to the attraction of O2 to an external magnetic field.