Question

Hexacyano complexes of metals in their +2 oxidation state are usually yellow while the corresponding hexaaqua compound are often blue or green, This is so because

• A. Hexacyano complexes absorb orange or red light thus appear yellow while hexaaqua complexes absorb indigo thus appear yellow
• B. Hexacyano complxes absorb indigo thus appearing yellow while hexaaqua complexes absorb orange or red light thus appear blue or green
• C. Hexacyano complexes absorb yellow light while hexaaqua complexes absorb blue light
• D. $CN^{-}$ions are yellow in colour while aque ions are blue or green in colour.

Answer 1

Answer: (B)

Hexacyano complxes absorb indigo thus appearing yellow while hexaaqua complexes absorb orange or red light thus appear blue or green

Answer 2

The ligand $CN^{-}$absorbs indigo, the high energy radiation and thus appears yellow. The aqua complexes have much smaller CFSE, they absorb orange or red light and thus appear green.