MHT CET Chemistry Question (2026) — Solution

Step-by-step solution

The crystal field splitting energy ( _0) depends on several factors, including the oxidation state of the central metal ion and the nature of the ligands. 1. Oxidation state of the metal ion: For the same metal and ligand, _0 increases with an increase in the oxidation state of the central metal ion. This is because a higher charge on the metal ion draws the ligands closer, leading to greater repulsion and a larger splitting of the d-orbitals. In complex I, Co is in the +2 oxidation state: [ Co(H _2 O) _6]^ 2+ . In complex II, Co is in the +3 oxidation state: [ Co(H _2 O) _6]^ 3+ . Therefore, _0 of II > I, which means I 2. Nature of the ligand: Strong field ligands cause a larger splitting than weak field ligands. CN ^- is a strong field ligand, whereas H _2 O is a weak field ligand. Thus, _0 of [ Fe(CN) _6]^ 3+ (IV) is significantly greater than that of [ Co(H _2 O) _6]^ 3+ (II) and [ Fe(H _2 O) _6]^ 3+ (III). The comparison IV 3. The comparison II Thus, the most appropriate and direct standard comparison is I Answer: I < II