Chapter 9 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals - 9-3 Molecular Orbital Theory - Applying Chemical Principles - Questions - Page 367: 5

See the answer below.

In the first two cases, the electron is removed from a bonding orbital, and in the last from an antibonding orbital. Since $B.O.=(N.\ Bonding -N.\ Antibonding)/2$ and that bond length decreases with bond order, the third case has a shorter bond because of the bigger bond order.