Copper (Cu) reacts with oxygen (O) to form copper oxide (Cu). The properties of copper oxide (CuO) are most likely Different from copper or oxygen
Similar to both copper and oxygen
Similar to only copper
Similar to only oxygen

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The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.