The correct order for the wavelength of absorption in the visible region is

Options

A. `[Ni(NO_(2))_(6)]^(4-) lt [Ni(NH_(3))_(6)]^(2+) lt [Ni(H_(2)O)_(6)]^(2+)`
B. `[Ni(NO_(2))_(6)]^(4-) lt [Ni(H_(2)O)_(6)]^(2+) lt [Ni(NH_(3))_(6)]^(2+)`
C. `[Ni(H_(2)O)_(6)]^(2+) lt [Ni(NH_(3))_(6)]^(2+) lt [Ni(NO_(2))_(6)]^(4-)`
D. `[Ni(NH_(3))_(6)]^(2+) lt Ni(H_(2)O)_(6)]^(2+) lt [Ni(NO_(2))_(6)]^(4-)`

Answer

A

Explanation

As all are octahedral complexes of the same metal (Ni), absorption will depend only on the nature of the ligand . From spectrochemical series, the CFSE of the given ligands are in the order `H_(2)O lt NH_(3) lt NO_(2)^(-)`
Hence excitation energies absorbed to show particular colour will be in the order `|Ni(H_(2)O_(6)|^(2+) lt |Ni(NH_(3))_(6)^(2+) lt |Ni(NO_(2))_(6)|^(4-)`
The wave length absorbed will be in the opposite order.