Comment on the $C-C$ bond length for ${\mathrm{C}}_2{\mathrm{H}}_6$ and ${\mathrm{C}}_2{\mathrm{F}}_6$ compounds.

Because of electronegative property of molecule $\mathrm{C}-\mathrm{C}$ bond length of ${\mathrm{C}}_2{\mathrm{H}}_6$ is greater than ${\mathrm{C}}_2{\mathrm{F}}_6$ .

So, the correct answer is $d_{\mathrm{C}-\mathrm{C}}\left({\mathrm{C}}_2{\mathrm{H}}_6\right)>d_{\mathrm{C}-\mathrm{C}}\left({\mathrm{C}}_2{\mathrm{F}}_6\right)$.
Hence, the correct answer is A.