Which phenomenon describes the movement of warm air rising due to temperature and density differences?

• A. Conduction
• B. Convection
• C. Radiation
• D. Diffusion

Answer: (B)

Convection is the movement of warm air rising because warmer air is less dense than the surrounding cooler air. When air is heated, it expands and becomes lighter, so it buoyantly rises. As it ascends, it cools, becomes denser, and the cooler air moves in to replace it, creating a looping convection current. This explains why you see rising warm air over an area and cooler air sinking or sweeping in to take its place, producing vertical mixing in the atmosphere or in a pot of heated liquid. Conduction requires direct contact for heat transfer through a substance; radiation moves heat via electromagnetic waves without needing a medium; diffusion is the spread of particles from high to low concentration, not a bulk movement driven by buoyancy.