What does cool and heavy material do in the mantle?

Correct answer: Sinks downward

In the mantle, material that cools generally becomes denser and heavier than the warmer material around it. Because of gravity, it moves downward or sinks. At the same time, hotter and less dense material tends to rise. These opposite movements help produce convection currents inside the Earth. Therefore, option D, sinks downward, is correct.

The key idea is density-driven movement. Heating makes mantle material expand and become relatively light, so it can rise; cooling makes it contract and become relatively dense, so it descends. This repeated rising and sinking forms a convection cycle. The material does not simply disappear, become an ocean, or fly upward after cooling. Although mantle movement is slow and occurs in solid material that can flow over long periods, the simplified school-level conclusion remains that cool, heavy material sinks.