Density is defined as mass per unit volume. The density of planets varies based on their composition. Terrestrial planets (Mercury, Venus, Earth, C. (1), (2) and (3) are correct D. All are correct Ans: A Accurate knowledge of geographical features (volcano locations), Earth's internal structure, planets and their moons, and space missions is required to answer this question. Mars) are primarily composed of rock and metal, making them relatively dense. Gas giants (Jupiter, Saturn, Uranus, Neptune) are primarily composed of lighter elements like hydrogen and helium, resulting in much lower densities. Among the options provided, Earth is a terrestrial planet and has the highest average density (approximately 5.51 g/cm³).