Answer:
Convection
Explanation;
Convection is on of the form heat transfer others being radiation and conduction.
Convection involves transfer of heat in fluids, that is gases and liquids. The transfer by convection is enhanced by convection currents.
Convection currents are circular paths through which the hot lighter fluid moves to the top and the denser cold fluid moves to the bottom. This enhances heat exchange between the hot fluid and the cold fluid as a result of temperature difference.
Therefore, convection is the type of heat transfer that explains why the air at the top floor of a building is hotter than the air at the bottom of the building.
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