Final answer:
Exponential decay is a type of decay where the quantity decreases by a constant factor over equal intervals of time. The function that represents exponential decay is of the form y = ab^x, where a is the initial quantity and b is the decay factor.
Step-by-step explanation:
Exponential decay is a type of decay where the quantity decreases by a constant factor over equal intervals of time. The function that represents exponential decay is of the form y = ab^x, where a is the initial quantity and b is the decay factor. In the given options, option a represents exponential decay because the radioactive activity decreases exponentially.