Final answer:
In an electrolytic cell, magnesium will get bigger while copper will get smaller. So in the electrolytic cell, the size of the copper will decrease.
Step-by-step explanation:
In an electrolytic cell, the size of the metal getting deposited on the cathode depends on the amount of metal ions in the solution.
As the concentration of metal ions increases, the size of the deposited metal increases.
Therefore, in the electrolytic cell, the size of the MG (magnesium) will get bigger as more magnesium ions are reduced to metallic magnesium and deposited on the cathode.
On the other hand, the size of the CU (copper) getting deposited on the cathode will get smaller as copper ions are reduced to metallic copper and deposited on the cathode.
So in the electrolytic cell, the size of the copper will decrease.