Question

Three complexes, [CoCl(NH3 )5] 2+(l) , [Co(NH3 )5H2O]3+(ll) and [Co(NH3 )6] 3+(lll) absorb light in the visible region. The correct order of the wavelength of light absorbed by them is :

A (I) > (II) > (III)

B (II) > (I) > (III)

C  (III) > (I) > (II)

D   (III) > (II) > (I)

Answer 1

Option A (I) > (II) > (III) is correct 

Explaination::

In a coordination compound, the strong field ligand causes higher splitting of the d-orbitals.Wavelength of the energy absorbed by the coordination compound is inversely proportional to ligand field strength of the given coordination compound. The decreasing order of ligand field strength is NH3 > H2O > Cl.Therefore decreasing order of wavelength absorbed is (I) > (II) > (III)