Which of the following species exhibits the shortest bond length for the nitrogen-nitrogen bond?

Solution

1. The bond order of ${\text{N}}_2$ is $3$ due to the triple bond.
2. The bond order of ${\text{N}}_2{\text{H}}_2$ is $2$ (double bond).
3. The bond order of ${\text{N}}_2{\text{F}}_2$ is $2$ (double bond).
4. The bond order of ${\text{N}}_2{\text{H}}_4$ is $1$ (single bond).
5. Higher bond order corresponds to shorter bond length, hence the answer is (C).