Explanation:

- In computer architecture, a stack-based CPU performs operations using a stack where instructions implicitly reference operands on top of the stack rather than using explicit memory addresses.

- Stack-based CPUs use zero-address instructions because operations are performed using the stack for data storage instead of separate memory addresses.

- Correct Answer: Option 2 - 0

- Option 1, 2 and Option 3, 1: Refer to one or two addresses in instruction, typical in accumulator-based or general-register architectures, not stack-based.

- Option 4, 3 and Option 5, 4: Uncommon, typically not utilized in stack or most common CPU architectures.