An object in a fluid experiences a buoyant force from the fluid. if the object is completely immersed, on which does the magnitude of this force depend on?

Weight of the fluid that the object displaces.

Explanation:

When the fluid is completely immersed in a fluid, it experiences pressure from all the direction. While the object is immersed in the fluid a force acts on it in the opposite direction, i.e., upwards. This force is termed as buoyant force.

Also, as per the Archimedes' Principle, the force experience by the object is the same as the weight of the fluid that gets displaced by the object.

Thus on complete immersion of the object in the fluid, it experiences the force same as the weight of the fluid that gets displaced