Question

[ni(cn)4]2- is colourless whereas[ni(h2o)6]2+ is green. why?

Answer 1

In [Ni(H2O)6]2+ there are unpaired electrons due to the un pairing of weak ligand(H2O). These electrons make d-d transition and give colour to the compound.In [Ni(CN)6]2- there is no unpaired electrons due to the pairing of electrons by the strong ligand(CN-). there is no free electron to make d-d transition so there is no colour to the complex