The correct answer is 3) Terrestrials are composed mostly of heavy elements.
Explanation:
Terrestrial planets in our Solar System include Mercury, Earth, Mars, and Venus, these planets are classified as "terrestrial" because all of them are composed of heavy materials especially of metals and rocks that made them different to gas giants that are composed of gases that are light elements. Additionally, terrestrial planets have a defined solid surface and a metallic central core. Also, they differ from other planets because they have no moon or few moons and the do not include a ring system. According to this, terrestrial planets can be described as those composed mostly of heavy elements (Option 3).
