Potassium ferrocyanide solution {K4[Fe(CN)6]} will give prussian blue colour when added to ferric chloride (FeCl3) due to formation of iron (III) hexacyanoferrate (II). FeCl3+K4[Fe(CN)6]───▶Fe4[Fe(CN)6]3 Iron (III) hexacyanido - ferrate (II) (Prussian blue colour)