What is the pressure in a 5 L tank with 1.5 moles of oxygen at 39.3 degrees Celsius?

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.

Answer/// he concludes that the atom particles can be broken due to the paddle wheel being moved by particles coming out of the metal;