For metal powders or metal alloys, if the reaction spreads over the whole length of the sample in 5 minutes or less, then it is assigned to which packing group?

• A. Packing Group III
• B. Packing Group 2
• C. Class 4.1
• D. Self-reactive substance

Answer: (B)

This item tests how packing groups for flammable solids (Class 4.1) are determined by how quickly a reaction can propagate along a sample. For metal powders or alloys, a propagation test checks whether the burning spreads over the entire length of the sample in five minutes or less. If it does, that material is placed in the middle category of hazard within Class 4.1—packing group II—meaning it has a medium level of danger: more hazardous than packing group III but not as dangerous as packing group I. If the spread is faster, it would be packing group I; if it is slower or does not propagate, it would be packing group III. The other options refer to broader classifications (the class itself) or related concepts (self-reactive substances) rather than the packing group assignment, so the five-minute propagation criterion best matches packing group II.