A parcel of air is buoyant when:

Question

BlackTom AI · Accepted Answer

Consider the concept of buoyancy in air parcels. 
Option 1: 'The parcel is cooler than the surrounding environment' would make the parcel denser than its surroundings, causing it to tend to sink rather than rise; thus this choice describes a non-buoyant or negatively buoyant scenario. 
Option 2: 'The parcel is at the same temperature as the environment' implies neutral buoyancy where there is no buoyant force driving upward or downward; in this case the parcel would neither rise nor fall due to thermal differences alone. 
Option 3: 'The parcel is warmer than the surrounding environment' is consistent with positive buoyancy: a warmer parcel is less dense than cooler surrounding air, so it experiences an upward buoyant force and tends to rise. This aligns with standard explanations of buoyancy in atmospheric contexts. 
Option 4: 'The air inside the parcel is saturated' speaks to humidity or moisture content, not directly to buoyancy. Saturation affects humidity and possibly condensation, but on its own does not determine whether the parcel is buoyant unless temperature and density relationships are also considered; hence it is not the defining criterion for buoyancy in typical dry-air buoyancy discussions.

A parcel of air is buoyant when:单项选择题

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