For diatomic molecules, the correct statement($s$) about the molecular orbitals formed by the overlap to two $2 p_z$ orbitals is(are)

$(A)$ $\sigma$ orbital has a total of two nodal planes.

$(B)$ $\sigma^*$ orbital has one node in the $x z$-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 $x y$-plane containing the molecular axis.

In which of the following transformations, the bond order has increased and the magnetic behaviour has changed ?

Correct decreasing order of bond order of oxygen species in $I$ to $IV$

$(I)$   $Na_2O_2$

$(II)$  $O_2 [AsF_6]$

$(III)$  $CsO_2$

$(IV)$  $O_2$

In which change bond order and number of unpaired $e^-$ both are increased

Molecular orbital theory was developed mainly by