What should an aircraft squawk if it is NORDO with additional system malfunctions?

When an aircraft experiences a situation where it is non-operational radio (NORDO) and has additional system malfunctions, squawking 7700 is appropriate because this transponder code indicates an emergency situation.

In aviation, squawking 7700 alerts air traffic control and other aircraft that the aircraft is experiencing an emergency, giving it priority in the airspace. This could include a variety of critical issues beyond simply losing radio communication, such as engine failure or other significant system malfunctions, making it vital for controllers and other pilots to be aware of the aircraft's distress.

The other squawk codes serve different purposes: 7500 indicates a hijacking or unlawful interference, 7600 specifically signifies a failure of communication (NORDO) without indicating any additional problems, and 7800 is not a standard transponder code in the context of emergency communications. Thus, squawking 7700 is the most suitable for situations where multiple serious issues are present beyond communication failure.