Given below are two statements: Statement (I): A solution of [Ni (...

In ${\left[Ni{\left({H}_{2}O\right)}_{6}\right]}^{2 +}$, ${H}_{2}O$ is a weak field ligand. Therefore, there are unpaired electrons in ${Ni}^{2 +}$. In this complex, the d electrons from the lower energy level can be excited to the higher energy level i.e., the possibility of $d - d$transition is present. Hence, ${\left[Ni{\left({H}_{2}O\right)}_{6}\right]}^{2 +}$ is coloured.

In ${\left[Ni{\left(CN\right)}_{4}\right]}^{2 -}$, the electrons are all paired as ${CN}^{-}$ is a strong field ligand. Therefore, $d - d$ transition is not possible in ${\left[Ni{\left(CN\right)}_{4}\right]}^{2 -}$. Hence, it is colourless.

${\left[Ni{\left({H}_{2}O\right)}_{6}\right]}^{+ 2} \to$Green colour solution due to $d - d$ transition.

${\left[Ni ( CN{)}_{4}\right]}^{- 2} \to$is diamagnetic and it is colourless.