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The features of the Molecular orbital theory are provided below.\tDuring the filling of electrons into molecular orbitals, the orbitals with the lowest energy levels are always the first to be filled. This selective filling of lower energy orbitals is commonly referred to as the Aufbau Principle.\tIn the molecular orbital theory, each of the molecular orbitals formed can only accommodate up to two electrons that have opposite spin. This is also called the Pauli Exclusion Principle.\tWhen two molecular orbitals have the same energy levels, electron pairing can only occur when both of these orbitals have one electron. This rule is often called Hund’s rule.\tThe molecular orbitals like atomic orbitals are filled in accordance with the Aufbau principle, Pauli’s exclusion principle, and the Hund’s rule.\tThe energy levels of bonding molecular orbitals are always lower than those of anti-bonding molecular orbitals. This is because the electrons in the orbital are attracted by the nuclei in the case of bonding MOs whereas the nuclei repel each other in the case of the anti-bonding MOs.

molecular orbital (MO) theory is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.