1.

[Ni(CN)_(4)]^(2-) is colourless whereas [Ni(H_(2)O)_(6)]^(2+) is green. Why ?

Answer»

Solution :`H_(2)O` is a weak LIGAND. 3d electrons of `Ni^(2+)` do not pair up. The unpaired electrons absorb red wavelength of white light for `d-d` transition and transmitted colour (complementary colour) is green. HENCE, the solution of `[Ni(H_(2)O)_(6)]^(2+)`is green.
`CN^(-)` is a strong ligand. The 3d electrons of `Ni^(2+)` pair up. There is no unpaired ELECTRON left to absorb ENERGY. Hence, solution of `[Ni(CN)_(4)]^(2+)` is colourless.


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