Final answer:
The function that represents exponential decay is f(x) = 2⁻¹. Hence, d) is correct.
Step-by-step explanation:
The function that represents exponential decay is f(x) = 2⁻¹
An exponential decay function is a function that decreases at a constant rate. In this case, the base of the function is 2 raised to the power of -1, which means it decreases by half every time x increases by 1.
For example, when x = 1, f(x) = 2⁻¹ = 1/2. When x = 2, f(x) = 2⁻² = 1/4. And so on.