The correct answer is B. 10 km/h.
A home signal is a railway signal that indicates whether a train is permitted to proceed into the next section of track. If a home signal is defective, it means that the train cannot proceed into the next section of track. In this case, the speed of the train while passing over the points shall not be more than 10 km/h. This is to ensure the safety of the train and its passengers.
Option A is incorrect because it is the speed limit for a train passing over points when the home signal is at danger. Option C is incorrect because it is the speed limit for a train passing over points when the home signal is at caution. Option D is incorrect because it is the speed limit for a train passing over points when the home signal is clear.