If 25mm of drywall has an R value of 0.5 and fiberglass insulation has an R value of 5 per inch and plywood has an R value of 0.25. What is the R value
of the wall with 4 inches of insulation?

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.