Question

$\lbrack Fe(CN)_{6}\rbrack^{4 -}$and $\left\lbrack Fe(H_{2}O)_{6} \right\rbrack^{2 +}$show different colour in dilute solutions because

• A. $CN^{-}$is a strong field ligand and $H_{2}O$is a weak filed ligand hence magnitude of CFSE is different
• B. Both $CN^{-}$and $H_{2}O$absorb same wavelength of energy
• C. Complexes of weak filed ligands are generally colourless
• D. The sizes of $CN^{-}$and $H_{2}O$are different hence their colour are also different.

Answer 1

Answer: (A)

$CN^{-}$is a strong field ligand and $H_{2}O$is a weak filed ligand hence magnitude of CFSE is different

Answer 2

$CN^{-}$is a strong field ligand hence pairing of electrons takes place while in case of $H_{2}O$pairing does not take place. Both ligands show different magnitude of crystal field splitting energy hence absorb different wavelengths and show different colurs.