What materials combined to form the topsoil?

weathered bedrock and wind-blown sand
decomposed humus and wind-blown sand
decomposed plant litter and weathered parent material
deposited sediment and decomposed plant litter

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.