Gas giant
The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope.
Ceres (dwarf planet)
Ceres (; minor-planet designation: 1 Ceres) is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter, slightly closer to Mars's orbit. With a diameter of , Ceres is the largest of the minor planets and the only dwarf planet inside Neptune's orbit. It is the 33rd-largest known body in the Solar System.