Which of the following describes convection?

Convection is the process of heat transfer that occurs in fluids, which include both liquids and gases, as a result of the movement of the fluid itself. The key aspect of convection is this movement—hotter areas of a liquid or gas become less dense and rise, while cooler areas sink, creating a continuous circulation pattern. This movement facilitates the transfer of heat from one part of the fluid to another.

In the context of the options provided, B is correct because it accurately captures this essential mechanism of heat transfer through liquids and gases due to movement. Other options fail to encompass the full nature of convection; for instance, describing heat transfer through solids relates to conduction, while heat transfer through electromagnetic radiation pertains to radiation. Additionally, stating that heat transfer only occurs in metals is misleading since convection can happen across various fluids, not merely through solid conductive materials.