Buoyancy independent of depth; drag reduces net force during ascent

Steps:

• Upthrust (buoyant force) equals weight of displaced water: ρ g V; ρ uniform, V constant for full immersion, so upthrust constant regardless of depth.
• Weight of sphere mg constant.
• When released, sphere accelerates upward; net (resultant) force = upthrust - weight - drag.
• Drag force increases with speed as sphere rises, so resultant force decreases.

Why B is correct:

• Upthrust constant by Archimedes' principle for uniform density; resultant force decreases as viscous drag rises with velocity.

Why the others are wrong:

• A: Resultant force decreases, not increases, due to growing drag.
• C: Upthrust constant, not decreasing.
• D: Upthrust constant, not decreasing.

Final answer: B