Question

what does convection require that is not required by other forms of heat transfer? it requires empty space to transfer heat. it requires moving gas or liquid to transfer heat. it requires objects to be in direct contact to transfer heat.

Explanation:

Convection is a mode of heat transfer. It specifically needs moving gas or liquid (fluids) as the medium. Radiation (another heat - transfer mode) can occur in empty space (like heat from the sun reaching Earth), so the first option is wrong. Conduction (another heat - transfer mode) requires direct contact between objects (e.g., heat transfer through a metal rod), so the third option is wrong.

Answer:

It requires moving gas or liquid to transfer heat.