Explain the energy level diagram for molecular orbitals formed by $1s$ orbitals.

(N/A) The $1s$ atomic orbitals on two atoms (e.g.,hydrogen) combine to form two molecular orbitals designated as $\sigma 1s$ and $\sigma^{*} 1s$.
$\sigma 1s$ is the bonding molecular orbital $(BMO)$ and $\sigma^{*} 1s$ is the antibonding molecular orbital $(ABMO)$.
The energy order is: Energy of $\sigma 1s < $ Energy of atomic orbital $1s  < $ Energy of $\sigma^{*} 1s$.
The sum of the energies of the molecular orbitals is equal to the sum of the energies of the two $1s$ atomic orbitals.
The energy diagram and the formation of these orbitals are shown below:
$AO =$ Atomic orbitals,$MO =$ Molecular orbitals
$BMO$ is formed by the constructive interference (addition) of atomic orbitals,while $ABMO$ is formed by the destructive interference (subtraction) of atomic orbitals.