Do mechanical waves require a medium to travel through? 10 pts, and explain .

Yes, because mechanical waves require an initial energy input, and without a medium energy cannot travel.

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.