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प्रश्न
Why a solution of [Ni(H2O)6]2+ is green while a solution of [Ni(CN)4]2− is colourless? (At. no. of Ni = 28)
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उत्तर
Ni has a valence shell electronic structure of 3d and is in the +2 oxidation state in both compounds. Two unpaired electrons do not couple up when weak-field water ligands are present. Due to the d-d transition, the [Ni(H2O)]2+ possesses two unpaired electrons, giving it a green hue.
The unpaired electrons in the third orbital pair up when a strong field cyanide ligand is present. The [Ni(CN)4]2 is colorless because there are no d-d transitions feasible because there are no unpaired electrons present.
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