AIIMS 2019 Chemistry Ligand Substitution Reactions MCQ Question

In Fe(CO)₅, the iron center can accommodate a maximum of 2 NO ligands due to the strong π-acceptor ability of NO, which allows it to replace CO ligands while maintaining the overall geometry. In Cr(CO)₆, the chromium center can replace up to 4 CO ligands with NO, as it can stabilize a higher oxidation state and accommodate more strong field ligands. Other options are incorrect because they either overestimate the number of CO ligands that can be replaced in Fe(CO)₅ or underestimate in Cr(CO)₆, failing to consider the electronic and steric factors influencing ligand substitution.