• # question_answer When pink ${{[Co{{({{H}_{2}}O)}_{6}}]}^{2\oplus }}$ is dehydrated the colour changes to blue. The correct explanation for the change is : A)  The octahedral complex becomes square planar.B)  A tetrahedral complex is formed.C)  Distorted octahedral structure is obtained.D)  Dehydration results in the formation of polymeric species.

Hydrated $CoC{{l}_{2}}.6{{H}_{2}}O$. is pink coloured and contains octahedral ${{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}$ ions. If this is partially dehydrated by heating, then blue coloured tetrahedral ions ${{[Co{{({{H}_{2}}O)}_{4}}]}^{2+}}$are formed.