The bond order of this molecule is 2.5.

How to see it step by step

For molecular orbital (MO) theory, bond order is given by the standard formula:

Bond order=(number of bonding electrons)−(number of antibonding electrons)2\text{Bond order}=\frac{(\text{number of bonding electrons})-(\text{number of antibonding electrons})}{2}Bond order=2(number of bonding electrons)−(number of antibonding electrons)​

You are told:

  • Bonding electrons = 8
  • Antibonding electrons = 3

So:

Bond order=8−32=52=2.5\text{Bond order}=\frac{8-3}{2}=\frac{5}{2}=2.5Bond order=28−3​=25​=2.5

Quick intuition

  • More electrons in bonding orbitals strengthen the bond.
  • Electrons in antibonding orbitals weaken it.
  • A bond order of 2.5 means the bond is stronger than a double bond but not as strong as a triple bond.

TL;DR: With 8 bonding and 3 antibonding electrons, bond order = (8−3)/2=2.5(8-3)/2=2.5(8−3)/2=2.5.