What are comets primarily made of?

Comets are primarily made of ice and dust, which is the correct choice. This composition is often described as a "dirty snowball" because comets contain a significant amount of frozen gases, including water vapor, carbon dioxide, ammonia, and methane, in addition to dust and small rocky particles. When a comet approaches the sun, the heat causes the ice to vaporize, leading to the development of a bright coma (a cloud of gas and dust surrounding the nucleus) and a tail that always points away from the sun due to solar wind and radiation pressure.

The other options do not accurately represent the primary composition of comets. Rock and metal are generally found in asteroids, not comets. Gas and liquid do not typically characterize the solid structures of a comet. While organic materials can be present, they are not the primary constituents compared to ice and dust. This distinctive ice-dust blend is what makes comets unique celestial bodies in our solar system.