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