Which method of heat transfer occurs in liquids or gases due to density differences?

The correct choice focuses on convection, which is the method of heat transfer that occurs in fluids, including liquids and gases, driven by differences in density. When a fluid is heated, it typically becomes less dense and rises, while cooler, denser fluid sinks. This movement creates a circulation pattern, allowing heat to be redistributed throughout the fluid.

In practical applications, convection occurs in various settings, such as in heating systems, atmospheric processes, and even in cooking. For example, when boiling water, the heated water at the bottom of the pot rises to the top, while the cooler water descends to take its place, forming a continuous cycle.

Conduction refers to heat transfer through direct contact between materials, where heat moves from a hotter object to a cooler one, but does not involve fluid movement and therefore does not rely on density differences. Radiation is the transfer of heat in the form of electromagnetic waves and does not require a medium, thus excluding fluids. Capillary action is a different phenomenon involving the movement of liquid through narrow spaces without assistance from external forces, primarily driven by adhesion and cohesion, not by density differences and thermal motion.