AX is a covalent diatomic molecule where A and X are second row...

Bond order of the covalent molecule, $AX$ is given as $2 . 5$, As $AX$ is a covalent diatomic molecule of second row elements of periodic table we can consider $CO, NO$ but bond order of $CO$ having $14$ electrons which is isoelectronic to nitrogen should be equal to $3$ and $NO$ having 15 electrons will have a bond order of $2 . 5$.

Molecular orbital configuration and bond order calculation of $NO$ is

ABMO= antibonding molecular orbital

Bond order =Number of bonding electrons $-$ number of anti bonding electrons.

Note: Total number of electrons equal to 13 will also have the 2.5 bond order. But in this case neutral diatomic molecule will not be possible