Answer: The three packing groups are:
Excepted Provisions (EP): These materials have no special packaging requirements and can be packaged using any appropriate method.
Limited Quantity (LQ): Materials in this group require packaging that minimizes the amount of material used and protects the contents during transport.
Ordinary Packaging (OP): Materials in this group require packaging that provides adequate protection against damage, leakage, and contamination during transport.
Since medium is not one of the three packing groups, we know that the required packaging must fall under either EP or LQ. Therefore, we need more information about the specific material being shipped to determine its proper packaging group and associated requirements.