Answer: D. A chemical change has occurred, because the chemical energy in the battery is transformed into magnetic energy in the iron.
Step-by-step explanation:
Krystal had to use a batter and a copper wire to make the nail attract other metal objects. As we know, the nail was not able to do this without these steps.
This means that the nail undergoes a chemical change to turn into a magnet.
Hope this helps! (If your answer is not D. then it's most definitely answer A. Physical change has occurred, because the chemical properties of the iron remain the same.)