AIIMS 2018 Chemistry Ligand Substitution Reactions MCQ Question

The reaction of [Cr(CO)₆] with excess NO leads to the formation of [Cr(NO)₄], as NO acts as a strong field ligand that can replace the CO ligands due to its ability to form stable complexes with chromium. In contrast, option (A) [Cr(CO)₆(NO)₂] is incorrect because it suggests an unstable intermediate rather than a stable product, while (C) [Cr(CO)₅]NO implies the presence of a free NO molecule rather than a coordinated ligand. Option (D) [Cr(CO)₂(NO)₄] is also incorrect as it suggests an unrealistic coordination environment for chromium with an excessive number of NO ligands compared to the stable product formed.