In which states of matter does convection primarily occur?

Convection is a process of heat transfer that occurs through the movement of fluid (liquids or gases). In convection, warmer regions of the fluid rise while cooler regions sink, creating a circulation pattern which effectively distributes heat throughout the fluid. This phenomenon is primarily observed in liquids and gases because these states of matter have the ability to flow and move freely, allowing for these convection currents to form.

In solids, the molecules are tightly packed and cannot move freely; hence, convection cannot occur. In contrast, both liquids and gases are composed of particles that are more loosely arranged, enabling them to move with relative ease. This characteristic is what allows convection to play a significant role in processes such as boiling water (liquid) or rising hot air (gas). Thus, the presence of fluid movement in both liquids and gases is fundamental to the convection process, making this the correct choice.