Which choice best describes a convection current?

The best description of a convection current is that it is the movement caused by density differences. Convection currents arise in fluids, which include both gases and liquids, when there is a variation in temperature, leading to differences in density. Warmer, less dense fluid rises, while cooler, denser fluid sinks. This cycle creates a continuous flow known as a convection current.

Option A is limited as convection does occur in both gases and liquids, not just gases. Option C is inaccurate because convection is distinct from conduction, which transfers heat through direct contact without bulk movement of fluid. Lastly, option D incorrectly implies that convection occurs at a constant temperature; in reality, temperature gradients are necessary to create the density differences that drive the convection process. Thus, the correct understanding focuses on the role of density differences in enabling the movement characteristic of convection currents.