13. The different substances in a mixture a. combine chemically
b. cannot be separated
C. form new molecules
d. keep their properties

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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.

The answer is solid copper 

It is a ok  i know i have a brain functioning well.