The transfer of thermal energy from one substance to another which requires no physical medium is

The transfer of thermal energy without requiring a physical medium is known as Radiation. This process involves the emission of electromagnetic waves, such as infrared radiation, which can travel through a vacuum. A prime example is how the Sun's heat reaches Earth across the vast emptiness of space.

• Conduction requires direct contact between substances for heat to transfer, like touching a hot metal spoon.
• Convection involves the movement of fluids (liquids or gases) to transfer heat, such as boiling water or air currents in a room. Both conduction and convection necessitate a material medium for energy propagation.
• Therefore, 'None of these' is incorrect as radiation perfectly describes the phenomenon.

Radiation is a crucial concept in understanding heat transfer in various environments.