What information does the UN number provide on a hazardous materials shipment?

The UN number serves as a unique identifier for hazardous substances, providing crucial information about the specific material's properties and associated hazards. Each UN number corresponds to a specific substance or a group of substances with similar dangerous characteristics, which aids in the identification of the material during transport. This identification helps first responders, transporters, and regulatory authorities understand the potential risks posed by the substance, enabling them to take appropriate safety precautions and response measures in the event of an incident. The other options provided do not encapsulate the primary function of the UN number; they focus instead on aspects such as weight, safety summaries, or shipping logistics, which are not encompassed within the UN numbering system.