Ni2+ has a turquoise color when dissolved in water due to the Ni(H2O)62+ ion. The six water molecules would here be ref

[answerhappygod]

Ni2+ has a turquoise color when dissolved in waterdue to the Ni(H2O)62+ ion. The six water molecules would here bereferred to as ligands of the metal. Adding some ammonia solutionchanges the color to light blue because ammonia molecules (ligands)take the place of the water ligands. Adding some ethylenediamine(H2NCH2CH2NH2, a common ligand for metal cations) will turn thecolor purple. Subsequently adding dimethylglyoxime[CH3C(=NOH)C(=NOH)CH3] then turns the color blood red, and, lastly,adding KCN to this now complex solution turns it the color orangeas cyanide becomes the ligand.
A) Le Chatelier can be used to explain this if each newligand binds tighter than the previous ligand: H2O < NH3 <ethylenediamine < dimethylglyoxime < CN-. In essence, the newligand can bind with the Co2+ when it is accessible and shift theequilibrium to the ligand that binds tighter.
B) These color changes are not about shiftingequilibrium, but about oxidation-reduction chemistry.
C) Ni2+ is a special case and these colorchanges can't be easily explained.
D) These color changes can't possibly have anything todo with shifting equilibrium, but just the addition of new colorsby reacting the new ligand with the available free cobaltcation.