Smallest to largest grain of salt coli bacteria human watermolecule skin cell

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.

Sorry i think the answer is b

What do you need with it’s not a question your just stating what it says

English , i don't understand spanish.