Question

${{[CoCl{{(N{{H}_{3}})}_{5}}]}^{2+}}$ (I),
${{[CoCl{{(N{{H}_{3}})}_{5}}{{H}_{2}}O]}^{3+}}$(II) and
${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ (III)
Absorb light in the visible region. The correct order of the wavelength of light absorbed by them is:
A. III > I > II
B. I > II > III
C. II > I > III
D. III > II > I

Answer 1

. While absorbing the frequency of the incoming light wave is at or near the energy levels of the electrons present in the matter. Then the electrons will absorb the energy of the light wave and change their energy state generally from ground to excited state or vice versa.

Complete step by step answer:
The tendency to absorb light generally depends on the strength of ligands present in the complex. Ligand can be defined as an ion or molecule that binds with a central metal atom to form coordination complexes. Complex having strong field ligands has a greater tendency to absorb light with higher energy.
Out of the three options ${{[CoCl{{(N{{H}_{3}})}_{6}}]}^{3+}}$ is a strong ligand that will absorb radiation of higher energy and have least wavelength as compare to other two.
${{[CoCl{{(N{{H}_{3}})}_{5}}{{H}_{2}}O]}^{3+}}$ is a weak field ligand as compare to I so it absorbs radiation of lesser energy and have wavelength higher than that of I.
${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ is weakest field ligand so it absorb light of least energy and higher wavelength as compare to I and II.
So, the correct answer is “Option B”.

Note: Strength of ligand whether it is strong field ligand or weak field ligand depends according to the series named as spectrochemical series in which ligands are arranged according to their strength. Series started from weak field ligands and ended with stronger one.