The bond length in CO is $1.128\text{Å}$. What will be the bond length of CO in $\mathrm{Fe}{\left(\mathrm{CO}\right)}_5$ ?

There is a synergistic link between Fe and CO in the compound $\mathrm{Fe}(\mathrm{CO}{)}_5$. The bond order of CO decreases as a result of metal and CO forming synergistic bonds. Bond length grows as bond order gets smaller. Option $\begin{array}{r}1.158\text{Å}\end{array}$  is the only one with a longer bond length than $1.128\text{Å}$  in this case. As a result, choice A is the right response.
Hence correct option A