Final answer:
The most active metal in terms of displacement reactions is Aluminum (Al).
Step-by-step explanation:
In terms of displacement reactions, the most active metal is the one that can easily replace another metal in a compound. The metal that is higher on the activity series will be the most active. In this case, the most active metal would be Aluminum (Al), since it is higher on the activity series than Copper (Cu), Zinc (Zn), and Calcium (Ca).