If the bond length of CO bond in carbon monoxide is $1.128\stackrel{0}{A},$ then what is the value of CO bond length in $Fe{\left(CO\right)}_5$?  

The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and the metal (Fe).
As the bond strength  $Fe\leftarrow C\equiv O$
Between Fe – C increases, the bond order between C-O decreases and the effective bonding can be represented as  $Fe=C=O$
This will increase the $C\text{ -\hspace{0.17em}}O$ bond length. Thus, the answers can be  $1.13\stackrel{o}{A}or1.15\stackrel{o}{A}$