Choose the correct order for `Delta_@` for the following complexes.
I) `[Co(H_2O)_6]^(2+)` II) `[Co(H_2O)_6]^(3+)` III) `[Fe(H_2O)_6]^(3+)` IV) `[Fe(CN)_6]^(3-)`

Options

A. `I lt II lt III lt IV `
B. `I lt III lt II lt IV `
C. `I lt II = III lt IV`
D. `I lt II lt IV lt III`

Answer

B

Explanation

`Delta_0` increase with increase of charge.
Among II and III, ligands are the same, charge of the cation same but `Z_(eff)` of `Co^(3+)` is greater than that of `Fe^(3+)`, In IV, `CN^(-)` is a strong field ligand, so, causes higher value of `Delta_0` .