Concept:Convection is the transfer of heat through the movement of fluids (liquids or gases), driven by density differences.
Explanation:In convection, a fluid is heated, becomes less dense, and rises, while cooler fluid sinks, creating a continuous circulation called a convection current.
When boiling water in a pot on a gas stove, the water at the bottom is heated first.
This heated water expands, becomes less dense, and rises to the top.
The cooler, denser water above sinks to the bottom to be heated again, forming a convection cycle.
This motion of the fluid itself carries heat throughout the pot — that is convection.
The other options involve different mechanisms:
Microwave ovens heat food by radiation (microwaves excite water molecules directly).
Feeling the warmth from the sun is radiation (heat travels through space via electromagnetic waves).
Heating a brass rod transfers heat by conduction (vibrations pass from molecule to molecule without fluid movement).
Only boiling water in a pot involves the bulk movement of a fluid (liquid water) and therefore exemplifies convection.
Answer:Boiling water in a pot on a gas stove.