What is the primary purpose of a mode C transponder in aviation?

The primary purpose of a mode C transponder in aviation is to respond to radar interrogations. Mode C transponders serve an essential role in air traffic control by sending information about an aircraft's altitude and identification back to ground-based radar systems. This information enables air traffic controllers to have a clear picture of aircraft positions and altitudes, enhancing situational awareness and safety in the skies.

In contrast, while weather data provision, navigation accuracy enhancement, and distance calculations are important aspects of aviation, they are not the specific functions of a mode C transponder. Weather data is typically provided through other systems, navigation accuracy can be improved using different technologies, and distance calculation is generally managed via on-board navigation systems rather than through radar transponder responses.