Final answer:
In a thermally isolated system, the aluminum experiences a greater magnitude gain or loss of heat compared to the copper.
Step-by-step explanation:
In a thermally isolated system consisting of a hot piece of aluminum and a cold piece of copper in thermal contact, the object that experiences the greater magnitude gain or loss of heat during the process of reaching thermal equilibrium is B) the aluminum.
This is because the specific heat capacity of aluminum is more than double that of copper. Specific heat capacity is a measure of how much heat energy is required to raise the temperature of a substance by a certain amount. Since aluminum has a higher specific heat capacity, it can absorb or release more heat energy compared to copper, resulting in a greater magnitude gain or loss of heat.