Acertain material has a density of 0.2 g/ml. is this material good for building a bridge or for making a cushion for a couch

Ithink is d. physical property

What? i don’t understand

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.