Final answer:
The percussion sound heard over empyema, which is pus in the lung, is dullness due to the liquid replacing air in the lung spaces.
Step-by-step explanation:
The percussion sound typically heard over empyema, which is pus in the lung, is dullness. Empyema affects the normally air-containing spaces within the lungs, replacing them with pus, which is a liquid. Sound waves are dampened more by liquid than by air, so when a healthcare provider taps (percusses) the chest wall over an area of empyema, the sound produced is less resonant and is described as dull. In contrast, resonance is a hollow sound typical of normal lung tissue, hyperresonance may be heard in cases of trapped air, such as in emphysema or pneumothorax, and tympany is a drum-like sound typically heard over a gas-filled stomach.