Which of the following is a key identifier for a Type A radioactive container?

The correct answer focuses on the weight limitation of Type A radioactive containers, which is a crucial aspect of their design and transportation specifications. Type A containers are specifically engineered to safely transport low-level radioactive materials. By regulation, these containers are designed to not exceed a maximum weight limit of 3,000 lbs when loaded. This is an essential characteristic that helps ensure safety during transport and indicates the container's intended use for materials that pose a lower risk compared to higher-class radioactive containers.

While metal drums and lightweight materials may be used in various contexts for packaging, they do not uniquely identify Type A containers. The weight limit is a regulatory requirement that directly pertains to the type of radioactive materials being transported. Similarly, the restriction of air shipment is not exclusive to Type A containers and does not serve as a distinguishing feature. Thus, the focus on the weight limitation as the key identifier is paramount for understanding Type A radioactive containers within HAZMAT operations.