Buoyancy is defined as:

• A. The rate of buoyant loss
• B. The pressure difference in water
• C. The ability to float, influenced by relaxation and lung volume
• D. The drag force in air

Answer: (C)

Buoyancy is the upward force that allows an object to float by displacing a volume of water equal to its weight. For a person, floating depends on density relative to water: more air in the lungs increases volume without adding much weight, making the body less dense and more buoyant. When you breathe out and your lungs hold less air, you become denser and sink more easily. Relaxation helps because relaxed muscles and a comfortable body position influence how your body displaces water and how easily the buoyant force can counteract your weight. That combination—lung volume increasing buoyant force and a relaxed body aiding flotation—best describes buoyancy. The other ideas either describe a different concept (pressure difference) or a force related to motion through air (drag), not the floating tendency itself.