What is the main type of motion observed in a convection current?

Convection currents are characterized by the circular motion that occurs as warmer, less dense fluid (like air or liquid) rises, while cooler, denser fluid sinks. This process creates a continuous loop or circulation pattern. In this motion, as the heated fluid rises, it loses heat to the surrounding environment and becomes denser, eventually sinking again. This cycle of rising and sinking fluids forms the basis of convection, leading to the characteristic circular flow known as a convection current.

The option indicating only horizontal or vertical motions misses the essential aspect of how fluids move in a cycle. While convection does involve both vertical and horizontal movements as part of the circular process, the defining feature is the circular motion created by the continuous rise and fall of fluids due to differences in temperature and density.