Final answer:
A person floating better in water when holding their breath is due to a decrease in gas volume, which lowers their density.
Step-by-step explanation:
When a person holds their breath, the volume of gas in their lungs decreases. According to Archimedes' principle, an object floats when its density is lower than the density of the liquid it is submerged in. When the volume of gas decreases, the person's average density decreases as well, making it easier for them to float in water.
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