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Correct increasing order for the wavelengths of absorption in the visible region for the complexes of $Co^{3+}$ is
Explanation
Stronger field ligand → larger $\Delta_o$ → shorter absorbed wavelength.
Detailed Solution
The order of the ligands in the spectrochemical series is $H_2O < NH_3 < en$.
Hence the wavelength of the light observed will be in the order $[Co(H_2O)_6]^{3+} < [Co(NH_3)_6]^{3+} < [Co(en)_3]^{3+}$.
Thus the wavelength absorbed will be in the opposite order, i.e. $[Co(en)_3]^{3+} < [Co(NH_3)_6]^{3+} < [Co(H_2O)_6]^{3+}$.