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

<li><strong>Option B: &quot;A is correct but R is incorrect&quot;</strong> is the right answer. Here is the reasoning:</li> </ol> <p><strong>Assertion A</strong> is correct. In the complex $\mathrm{Ni(CO)_4}$, if we assume the oxidation state of Ni to be x, we can set up the equation:</p> <p>$ x + (0 \times 4) = 0 $</p> <p>From which we find that (x = 0).</p> <p>Similarly, in $\mathrm{Fe(CO)_5}$, if we let the oxidation state of Fe be y, the equation becomes:</p> <p>$ y + (0 \times 5) = 0 $</p> <p>Solving this gives (y = 0).</p> <p>Therefore, the oxidation states of both Ni and Fe are zero in their respective complexes, verifying that Assertion A is true.</p> <p>Regarding <strong>Reason R</strong>, it is incorrect. The low oxidation states in these complexes are stabilized through synergic bonding, which involves the ligand being a $\pi$-acceptor, not a $\pi$-donor. The CO ligand in these complexes accepts electron density from the metal into its antibonding molecular orbitals, characterizing a $\pi$-acid ligand, and not a $\pi$-donor ligand as stated. Consequently, Reason R does not hold true.</p>