Final answer:
The mass of an adult bullfrog is reasonably estimated at 0.5 kg, with options 0.5 mg and 0.5 g being too light, and 5 kg being too heavy for an adult bullfrog.
Step-by-step explanation:
A reasonable estimate for the mass of an adult bullfrog would be option b) 0.5 kg. This estimate aligns well with the general mass of a large adult bullfrog, which can vary but typically stays under a kilogram. To consider the other options, 0.5 mg is far too light, as it would be a mass suitable for something microscopic, and 0.5 g, while within the gram range, is still too light for an adult bullfrog. On the other end, 5 kg is too heavy, as this would approach the mass of some larger domesticated animals like dogs or cats.