Which species has the shortest bond length?

The species with the shortest bond length among the choices is carbon monoxide (CO). The bond length in a molecule is influenced by several factors, including the type and number of bonds formed between atoms as well as the sizes of the atoms involved.

In CO, the molecule has a triple bond between the carbon and oxygen atoms. A triple bond consists of one sigma bond and two pi bonds, resulting in a stronger and shorter bond compared to double or single bonds. The effective overlap of orbitals in triple bonds allows the atoms to be pulled closer together.

In contrast, while nitrogen (N2) also has a triple bond, the electronegativity difference between carbon and oxygen is smaller compared to that between two nitrogen atoms, allowing CO to achieve a slightly shorter bond length due to its molecular structure. The other options, O2 and F2, feature double and single bonds respectively, which are inherently longer. O2 has a double bond, while F2 has a single bond, leading to longer bond lengths compared to the triple bond found in CO and N2.

Thus, the combination of the strong triple bond and the specific atomic characteristics of carbon and oxygen contributes to CO having the shortest bond length among the given species.