The fastest mode of heat transfer is radiation.

Explanation:
Heat transfer is the process of the exchange of thermal energy between two or more objects or systems. There are three main modes of heat transfer: conduction, convection, and radiation. Each mode has its own characteristics and speed of transfer.

1. Conduction:
Conduction is the transfer of heat through direct contact between two objects or substances. It occurs due to the collision of particles and the transfer of kinetic energy. In this process, heat is transferred from the region of higher temperature to the region of lower temperature. However, conduction is relatively slower compared to the other modes of heat transfer.

2. Convection:
Convection is the transfer of heat through the movement of a fluid (liquid or gas). It involves the bulk movement of molecules within the fluid, which carries thermal energy from one place to another. Convection can occur through natural (gravity-driven) or forced (mechanical) means. While convection is faster than conduction, it is still comparatively slower than radiation.

3. Radiation:
Radiation is the mode of heat transfer that does not require any medium for transmission. It occurs through electromagnetic waves, such as infrared radiation, visible light, ultraviolet radiation, and so on. Unlike conduction and convection, radiation can occur even in a vacuum. This mode of heat transfer is the fastest because electromagnetic waves travel at the speed of light.

Key Points:
- Radiation is the fastest mode of heat transfer.
- It occurs through electromagnetic waves.
- Radiation can occur in a vacuum.
- Electromagnetic waves travel at the speed of light, making radiation the fastest mode.
- Conduction and convection are comparatively slower modes of heat transfer.

In conclusion, radiation is the fastest mode of heat transfer. It occurs through electromagnetic waves and does not require any medium for transmission, making it faster than conduction and convection.