BONDING IN METAL CARBONYLS

In metal carbonyls, there is synergic bonding interaction between metal and carbon monoxide. This leads to increase in strength of metal ligands bond and decrease in bond order of CO in carbonyl complex as compared to bond order in carbon monoxide. Simple carbonyls are invariably spin-paired complexes except for vanadium metal. Which one of the following metal carbonyls are inner orbital complexes with diamagnetic property ? (P) Ni(CO)_(4)" "(Q) Fe(CO)_(5) (R ) V(CO)_(6)" "(S) Cr(CO)_(6) Select the correct answer from the codes given below :

The figure represents the synergic bonding interaction in metal carbonyl complex. On the basis of the explain the following: (i) Strength of Metal-ligand bond (ii) Bond order of CO in carbonyl complex as compared to bond order in carbon monoxide.

Assertion: Oxidation state of Fe in Fe(CO)_(5) is zero. Reason: Synergic bonding takes place in this metal carbonyl complex.