Universal Postal Union Convention allows only the following dangerous goods to ship by mail?

• A. Radioactive Material
• B. Infectious Substances
• C. Ammunition
• D. Lithium Ion Batteries in Equipment

Answer: (D)

The key idea here is how the postal system handles dangerous goods. Under the Universal Postal Union rules, most dangerous materials cannot be mailed at all; only a very limited set of items are allowed if properly packaged and documented. The one category that is permitted is lithium ion batteries that are contained in equipment—meaning the battery is installed inside a device, not shipped as a loose battery.

This is allowed because keeping the battery inside a device reduces the risk of short circuits, punctures, or leaks, and it can be packaged with appropriate safeguards and labeling under the Dangerous Goods by Mail rules. By contrast, radioactive materials, infectious substances, and ammunition involve higher hazards or require specialized handling and facilities that the postal network cannot provide, so they are not allowed in regular mail.