A solution of `[Ni(H_(2)O)_(6)]^(2+)` is green but a solution of `[Ni(CN)_(4)]^(2-)` is colourless Explain.

Explanation

Formation of `[Ni(H_(2)O)_(6)]^(2+)`

Since `H_(2)O` molecules represent weak field ligands, they donot cause any electron pairing. As a result the complex has two unpaired electrons and is coloured. The d-d transitions absorb radiations corresponding to red light and the complemenmtary colour emitted is green .
Formation of `[Ni(CN)_(4)]^(2-)` . for the details of the structure of the complex,. since the complex has no unpaired electrons there is no scope for and d-d transition . the complex is therefore, colourless .