GED Science Practice 2025 – 400 Free Practice Questions to Pass the Exam

The definition of a "planet" in our solar system is best captured by the concept of a celestial body that orbits a star, specifically a sun, and meets certain criteria, such as being massive enough to be rounded by its own gravity. The correct answer emphasizes that planets are primarily composed of materials like rock and metal and have a stable orbit around the sun.

In the context of the other choices, they do not accurately capture the essence of what a planet is. The first describes small organisms in water, which is unrelated to celestial bodies. The second involves the synthesis of compounds and energy, which pertains to chemical processes rather than planetary characteristics. The third option, while mentioning celestial bodies around a star, doesn’t address the material composition or the definition required for a planet. Thus, the focus on composition and orbital behavior in the correct choice aligns with the established scientific understanding of planets in our solar system.