Among the following, the molecule with bond order one is

According to molecular orbital theory, the bond order of a molecule can find from the following formula:

Bond order = $\frac{1}{2}$ × [No.of e− s in B.O − No.of e− s in anti B.O)

From molecular orbital diagram, the bond order is 3 for ${\mathrm{N}}_2$ molecule

For O2 molecule the bond order is 2.

For hydrogen molecule, the molecular orbital diagram is as follows:

Now, Bond order of ${\mathrm{H}}_2$= $\frac{1}{2}$× (2 −0)=1