Final answer:
If our Sun was the size of Betelgeuse, its extended atmosphere would reach past the orbit of Jupiter, indicating that Jupiter is the correct answer.
Step-by-step explanation:
If our sun was the size of Betelgeuse, it would reach out as far as the planet Jupiter. From the information provided, Betelgeuse's surface would stretch past the orbit of Mars and engulf it, as well as Earth. Betelgeuse is so large that, if placed at the center of our solar system, its extended atmosphere would reach past the orbit of Jupiter according to the model illustrated by the Hubble Space Telescope image. Hence, the correct answer to which planet the sun would reach out to if it was the size of Betelgeuse is b) Jupiter.