Which physical property is being used to separate the mixtures in each of the following cases? a) a magnet is used to separate iron filings from sand. b) fat is skimmed off the top of a sauce. c)a sample of ocean water boiled until only salt remains.

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.

What is the gold assay