Question -
Answer -
In [Ni(H2O)6]2+,
isa weak field ligand. Therefore, there are unpaired electrons in Ni2+.In this complex, the d electrons from the lower energy levelcan be excited to the higher energy level i.e., the possibility of d−d transitionis present. Hence, Ni(H2O)6]2+ iscoloured.
In [Ni(CN)4]2−, the electrons are all paired as CN– is a strong field ligand. Therefore, d-d transitionis not possible in [Ni(CN)4]2−. Hence, it iscolourless.