This sequence represents the various chemical species that can be formed by the oxidation of copper (Cu) in the presence of different reactants.

CuSO4 - Copper (II) sulfate, a chemical compound containing copper in its +2 oxidation state, commonly used in electroplating and as a fungicide.

Cu - Metallic copper, the pure form of copper with no oxidation state.

Cu(NO3)2 - Copper (II) nitrate, another chemical compound containing copper in its +2 oxidation state, commonly used in various industrial processes.

Cu(OH)2 - Copper (II) hydroxide, a chemical compound formed when copper reacts with bases or aqueous solutions containing hydroxide ions.

CuO - Copper (II) oxide, a black solid compound formed when copper reacts with oxygen in the air.

CuSO4 - Reverting back to copper (II) sulfate, completing the cycle of oxidation and reaction with different compounds.