Which of the following is a process in which hot, less dense materials rise upward and are replaced by colder, more dense materials?

Convection

The correct answer is option 4. Convection.

The process in which hot, less dense materials rise upward and are replaced by colder, more dense materials is Convection.

Convection is a mode of heat transfer that occurs through the movement of fluids (liquids or gases). In the context of fluid dynamics, convection involves the transfer of heat energy by the movement of the fluid itself. In a fluid, such as air or water, when one part is heated, it becomes less dense and rises, while the cooler, denser part sinks. This creates a circulation pattern where hot materials rise and cold materials sink, leading to the transfer of heat energy throughout the fluid. This process is commonly observed in phenomena such as the rising of warm air currents, the circulation of ocean currents, and the movement of magma in the Earth's mantle.