What type of airspace requires a transponder for transit?

The requirement for a transponder is particularly relevant in Class B and Class C airspace. In Class B airspace, which encompasses the airspace around busy airports, a transponder is necessary to help air traffic control (ATC) monitor and manage the high volume of traffic safely. It provides critical information, including altitude and identification, which aids in maintaining a safe distance between aircraft.

Similarly, in Class C airspace, which typically surrounds airports with a moderate level of traffic, a transponder is also required. This ensures that ATC can maintain situational awareness and effectively communicate with all aircraft operating within that space. The transponder enhances safety by contributing to radar services that are essential for both separation and avoidance of potential conflicts.

While Restricted airspace and Class D airspace may have operational requirements, they do not universally necessitate a transponder for transit. Restricted airspace is generally defined for specific purposes, and although entering such areas may require communication with ATC, a transponder is not always mandated. Class D airspace, primarily surrounding smaller airports, does require communication with ATC, but does not uniquely require a transponder for all operations. Thus, Class B and Class C airspace's requirements make them the correct answer in the context