The correct option is A 1.158 oA
In free carbonyl, there will be no back bonding and the bond order of 'C-O' is 3.
In Fe(CO)5, there will be back boding due to donation of electron from metal orbital to the carbonyls. Due to back bonding the bond order of 'M-C' increases and bond order of 'C-O' decreases. This result in increase in bond length of the 'C-O' than the free carbonyl.
Hence, only option (a) value is higher than 1.128oA.
Therefore, option (a) is correct.