Which of the following items is only permitted in checked baggage?

• A. Small clinical thermometer
• B. E-cigar
• C. Spare lithium battery
• D. Permeation device

Answer: (A)

The small clinical thermometer is the correct answer because certain types of thermometers, particularly those containing mercury, are subject to strict regulations regarding their transportation. Airlines generally allow these types of thermometers only in checked baggage to avoid potential spills and hazardous exposures in the cabin.

Checked baggage undergoes different handling practices than carry-on luggage, which is subjected to more strict regulations due to the proximity of passengers. Placing these items in checked baggage mitigates the risk of exposure to other passengers and crew during the flight.

In contrast, e-cigars and spare lithium batteries typically have guidelines that allow for their transportation only in carry-on luggage due to the potential fire hazards they pose. Permeation devices may have specific regulations based on their intended use and the materials involved, which can also restrict them to checked baggage in some cases but are not as universally applicable as clinical thermometers. Thus, the small clinical thermometer stands out as the item that is specifically allowed only in checked baggage.