c
\(Z n_{2}\left[F e(C N)_{6}\right], K_{3}\left[C o\left(N O_{2}\right)_{6}\right] \) and \(\left(N H_{4}\right)_{3} A s\left[M o_{3} O_{l 0}\right]_{4}\) show color due to d-d transition while \(B a C r O_{4}\) is coloured due to charge transfer phenomenon.

Further according to spectrochemical series the strong ligand possessing complex has higher energy and hence lower wavelength. Therefore, complexes containing \(N O_{2}, N H_{4}^{+}, O^{2-}\) etc., ligands show yellow colour while \(\mathrm{CN}^{-}\) forces the complex to impart white colour.

Spectrochemical series \(I^{-} < B r^{-} < S^{2-} < S C N^{-} < C I^{-} < N O_{3}^{-} < N_{3}^{-} < F^{-} < O H^{-}\)

\( < C_{2} O_{4}^{2-}=H_{2} O < N C S^{-} < C H_{3} C N < p y < N H_{3} < e n\)

\( < b i p y <  phen  < N o_{2}^{-} < p p h_{3} < C N^{-}=C O\)