Which is not true about metal carbonyls?

Given below are two statements: one is labelled as “Assertion A” and the other is labelled as “Reason R”

Assertion A : In the complex $\mathrm{Ni}(\mathrm{CO}{)}_4$ and $\mathrm{Fe}(\mathrm{CO}{)}_5$, the metals have zero oxidation state.

Reason R : Low oxidation states are found when a complex has ligands capable of $\pi$-donor character in addition to the $\sigma$-bonding.

In the light of the above statements, choose the most appropriate answer from the options given below

Among the given complexes that possess "$\mathrm{CO}$" ligand bridges are

$\underset{\mathrm{I}}{\left[{\mathrm{Co}}_2{\left(\mathrm{CO}\right)}_8\right]} \underset{\mathrm{II}}{ \left[{\mathrm{Fe}}_3{\left(\mathrm{CO}\right)}_{12}\right]} \underset{\mathrm{III}}{\left[{\mathrm{Mn}}_2{\left(\mathrm{CO}\right)}_{10}\right]} \underset{\mathrm{IV}}{\left[{\mathrm{Fe}}_2{\left(\mathrm{CO}\right)}_9\right]}$