Which of the following describes what would have happened to jupiter if it were 80 times larger?
a) it would be unstable to rotate?
b) it would become a sun?
c) it would become a star?
d) it would become a supernova?

What would happen if Jupiter was 80 times larger?

The answer is: C) it would become a star, assuming of course its mass grows as well by a factor of 80, not just it's volume.

It would become a red dwarf star in fact.

It would still rotate (as our Sun does), although it's not the same way as our Earth rotates, because movements of gases are different than movement of solid masses.

it wouldn't become a sun because its temperature wouldn't be warm enough.

It wouldn't become a supernova, because that's basically a dying star... a 80-times larger Jupiter would become a new star, not a dying one.