Chemistry - Coordination Chemistry Question with Solution | TestHub

Refined Solution:

The metal-carbon bond order is highest when the metal has the highest electron density available for $\pi$-backbonding to the CO ligands. This strengthens the M-C bond and weakens the C-O bond. Ni(0) ($d^{10}$) has the highest electron density among the metals in the options. In $[Ni(CO{)}_3(PM{e}_3)]$ (C) and $[Ni(CO{)}_3(PP{h}_3)]$ (D), Ni is in the 0 oxidation state and has only three CO ligands, allowing for substantial backbonding to each CO. This results in the highest metal-carbon bond order.

The final answer is $\boxed{C}$