Question

As an object sinks in a fluid, the buoyant force ____.

Answer 1

Increases, until the object is fully submerged.

By Archimedes' Principle, the buoyant force is equal to the weight of the fluid displaced by the object.

Answer 2

The net force f = ma = B - W on an immersed object of weight W. So when B < W so that f = ma < 0 the object has acceleration a < 0 which is downward when W and g < 0. That is the object accelerates downward because the buoyancy is insufficient to offset the weight of the object.

As an object sinks in a fluid the buoyant force on it would remain the same.