Why does hot material rise in a convection current?

Correct answer: Because its density decreases

Convection is the movement of material caused by differences in temperature and density. When a substance is heated, its particles usually move farther apart, so the substance expands. The same amount of material then occupies more space, and its density decreases. It becomes relatively lighter than the cooler material around it and tends to rise. Therefore, option A is correct. The other choices describe unrelated changes: hot material does not necessarily become stone, ice or a river.

In a convection current, heating at the lower part makes material less dense, so it rises. As it moves away from the heat source, it can cool, become denser and sink again. This rising and sinking creates a circulating movement. In Earth science, such movements in the mantle are discussed as a possible mechanism connected with the movement of tectonic plates. The key chain is heating, expansion, lower density and upward movement. Since option A states the essential reason, it is the correct choice.