Which term describes the force exerted by a fluid on an object placed in it?

The correct term that describes the force exerted by a fluid on an object placed in it is buoyant force. This force arises due to the difference in pressure exerted by the fluid on different parts of the submerged object. According to Archimedes' principle, the buoyant force is equal to the weight of the fluid displaced by the object. This means that when an object is placed in a fluid, it experiences an upward force that can cause it to float or rise within the fluid if this force is greater than the object's weight.

The other terms relate to fluid behavior but do not specifically describe the force exerted by a fluid on an object in the same way. Hydrostatic pressure refers to the pressure exerted by a fluid at rest due to the weight of the fluid above it, fluid dynamics deals with the behavior of fluids in motion, and viscosity describes a fluid's resistance to flow or deformation. While all these concepts are integral to understanding fluid mechanics, only buoyant force directly pertains to the query about the force on an object in the fluid.