Question

In metal carbonyls. There is synergic bonding interaction between metal and carbon monoxide . This leads to increase in strength of metal ligand bond and decrease in bond ordeer of CO in carbony1 complex as compared to band order in order in carbon monoxide.
The increases in bond length in CO as compared to carbon monoxide .is due to :
A. the donation of lone pair of electrons from a filled d-orbital of the metal atom
B. the donation of pair of electrons from a filled d-orbital of metal into the vacant antibonding `pi^(*)` orbital of carbon monoxide.
C. (A) and (B)
D. None

Answer 1

(B), Donation of electrons from a filled d-orbital of metal into the vacant antibonding `pi^(**)` bonding orbital of CO decrease the bond other three to two and half or slightly more thus increasing the bond length between C-O.
Bond order `prop (1)/("Bond length")`