Final answer:
The upthrust or buoyant force on a floating object is equal to the weight of the object, as stated by Archimedes' principle, which explains why the object floats rather than sinks or rises. The correct answer is option C.
Step-by-step explanation:
When an object floats in a liquid, the upthrust on it, also known as the buoyant force, is a critical concept in understanding flotation and buoyancy. The upthrust on an object, when it floats in a liquid, is equal to the weight of the body. This is known as Archimedes' principle, which states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.
Therefore, for an object to float, this buoyant force must at least be equal to the weight of the object itself. In the case of an object floating on the surface of a fluid, the upthrust is equal to the weight of the body (option c), allowing it to float without sinking or rising.