D. When its weight is equal to the buoyant force exerted by the water.
Explanation:
A fluid exerts an upward force on a body submerged in it. This force that tends to lift the body is called floating force.
The flotation force that acts on a body submerged in a fluid is equal to the weight of the fluid displaced by the body and acts upward passing through the centroid of the displacemented volume.
