Are mercurial barometers freely allowed as checked baggage?

Mercurial barometers are considered dangerous goods because they contain mercury, a hazardous substance. Due to the risk of leakage or breakage, which could pose serious health and environmental hazards, regulations prohibit the transport of such items in checked baggage. Instead, they are generally allowed only in carry-on baggage, where they can be more easily monitored by the traveler. This precaution helps to mitigate the risks associated with mercury exposure during transport, ensuring safety for both airline personnel and other passengers.

The other options suggest scenarios where mercurial barometers could be transported without restrictions or under specific conditions, which is not in line with the safety protocols established for hazardous materials in air travel.