Given the field strength order CN- > NH3 > H2O > F-, which complex absorbs its d-d band at the shortest wavelength?

JEE Main levelSingle correct optionDifficulty 2 of 3cc098

Given the field strength order $CN X^{-} > NH X_{3} > H X_{2} O > F X^{-}$ , which complex absorbs its d-d band at the shortest wavelength?

All four are octahedral Co(III). The strongest field ligand gives the largest

Δ_{o}

, and since

λ \propto 1/ Δ_{o}

, the largest splitting means the shortest wavelength. That is the cyanido complex.