From left to right, aqueous solutions of:  cobalt(II) nitrate, Co(NO<sub>3</sub>)<sub>2</sub> (red); potassium dichromate, K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> (orange); potassium chromate, K<sub>2</sub>CrO<sub>4</sub> (yellow); nickel(II) chloride, NiCl<sub>2</sub> (green); copper(II) sulfate, CuSO<sub>4</sub> (blue); potassium permanganate, KMnO<sub>4</sub> (violet).
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