Consider the following statements.
$I$. In the conversion of $O_2$ to $O_2^{2+}$,bond order decreases.
$II$. In the conversion of $O_2$ to $O_2^{2+}$,magnetic property is not changed.
$III$. In the conversion of $O_2$ to $O_2^{2+}$,bond length decreases.
$IV$. $O_2^{2-}$ and $B_2$ have same bond order.
Identify the correct statements.

Which of the following molecules does not exist according to molecular orbital theory?

During the conversion of peroxide ion $(O_2^{2-})$ to superoxide ion $(O_2^-)$,an electron is removed from which of the following molecular orbitals?

The bond order of $He_2^+$ molecule ion is

For diatomic molecules,the correct statement$(s)$ about the molecular orbitals formed by the overlap of two $2p_z$ orbitals is(are):
$(A)$ $\sigma$ orbital has a total of two nodal planes.
$(B)$ $\sigma^*$ orbital has one node in the $xz$-plane containing the molecular axis.
$(C)$ $\pi$ orbital has one node in the plane which is perpendicular to the molecular axis and goes through the center of the molecule.
$(D)$ $\pi^*$ orbital has one node in the $xy$-plane containing the molecular axis.

Which of the following concepts is $NOT$ part of the valence bond theory $(VBT)$?