How can we represent changes in a chemical structures during a chemical reaction?

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.

B"hf and f-"  is the correct answer took the test on edgenuity and got it right     

Idon't know hope someone you