About Trailer coupling and licence plate: which statement is WRONG?
Trailers with a breakaway braking device may NOT also have an auxiliary coupling; the two work in opposite ways (book p.231) and combining them is a defect, not extra safety.
The coupling of every trailer must always have an approval mark and be properly fastened, regardless of weight or which braking device was chosen.
An auxiliary coupling is a valid alternative to a breakaway braking device for any trailer, regardless of weight.
It is exactly the reverse. Up to 750 kg: white plate with the towing car's registration. Above 750 kg: own registration certificate with a yellow plate and its own registration number.
Explanation
Book p.231 - the choice (breakaway device OR auxiliary coupling) only applies up to 1,500 kg; above 1,500 kg a breakaway braking device is mandatory and an auxiliary coupling alone does not suffice.