The number of bridging $CO$ ligand$(s)$ and $Co-Co$ bond$(s)$ in $Co_2(CO)_8$ respectively are

Give an example of synergistic bonding interaction in a carbonyl complex.

The bond length of the $C-O$ bond in carbon monoxide is $1.128 \ \mathring{A}$. The $C-O$ bond length in $Fe(CO)_5$ is ............. $\mathring{A}$.

Zeise's salt is

The metal which does not form a polynuclear carbonyl is

The correct pair of orbitals involved in $\pi$-bonding between metal and $CO$ in metal carbonyl complexes is