Which of these accurately describes a chemical reaction? A. Products and reactants combine to form new reactants
B. Products and reactants combine to form new substances
C. Products combine to make reactants
D. Recatants combine to form products

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.

Is a logical series of steps