The rising of hot mantle material shows which process in a convection cycle?

Correct answer: Rising due to decreasing density

Heating changes the density of mantle material. When mantle material becomes hot, it generally expands and becomes less dense than the cooler material around it. The less-dense material experiences an upward tendency, so it rises. This rising movement is one part of a convection cycle. Option B correctly describes rising because of decreased density. Option A describes the opposite stage: cooler material can become denser and sink, but it does not explain the rising hot material asked about here.

The sequence can be understood through the relation between temperature and density. Heating usually lowers density, and cooling usually raises density, although the mantle is solid and moves extremely slowly over long periods. Thus, the question is not about ocean water freezing or continents simply remaining fixed. It asks what the upward movement represents, and the correct process is buoyant rise caused by lower density. The supplied answer B is scientifically appropriate and the explanation correctly connects heat, density, and upward motion.