`[Fe(CN)_(6)]^(4-)` and `[Fe(H_(2)O)_(6)]^(2+)` are of different colours in dilute solutions why?
A. `CN^(-)` is a strong field ligand and `H_(2)O` is a weak field ligand hence magnitude of CFSE is different
B. both `CN^(-)` and `H_(2)O` absorb same wavelength of energy
C. complexes of weak field ligands are generally colourless
D. the sizes of `CN^(-)` and `H_(2)O` are different hence their colours are also different .