Which of the following indicates an emergency situation aboard a boat?

Orange smoke blowing from a boat is a strong indicator of an emergency situation. This type of signal is specifically associated with distress and is recognized universally as a means of alerting others to a need for assistance. In maritime distress signaling, orange smoke is particularly effective because it is easily seen, even in challenging weather conditions and at a distance, making it an effective way to communicate that someone is in trouble.

While white smoke, loud horns, and flashing lights can all have specific meanings in different contexts, they do not universally indicate an emergency. For instance, white smoke might just be related to normal operations or even a minor issue. A loud horn can serve various purposes such as signaling a turn or warning of navigational hazards, rather than specifically indicating distress. Flashing lights, while they can indicate a vessel is signaling or in motion, do not necessarily convey an emergency situation unless they are part of a distress signal protocol.

Thus, the use of orange smoke is distinctly tied to emergencies, which is why it is the correct choice in identifying an emergency situation aboard a boat.