8.2  Describe the ways the giant planets differ from the terrestrial planet.

Much larger, both overall size and mass, but their densities are much lower - closer to that of water than that of rock, like the terrestrial planets.  They're made primarily of lighter elements - hydrogen, helium, carbon, oxygen, and nitrogen, much more like the Sun (especially Jupiter) than the terrestrial.

8.8  Three of the giant planets radiate into space approximately twice as much energy as they absorb from the Sun.  What is the source of this excess energy?

Some of Jupiter's energy is left over from it's formation.  All of the planets are still condensing and differentiating to varying degrees.