Which label indicates the nature of the substance in a Category A label?

A Category A label is specifically designed to convey critical information about the dangerous goods being transported, and it includes an inscription that indicates the substance's identity and potential hazards. This inscription plays a vital role in ensuring that individuals handling the dangerous goods understand what they are dealing with, allowing them to take appropriate precautions.

The inscription typically includes the UN number, the proper shipping name, and any associated hazard statements, which together provide immediate recognition of the substance and its risks. This clear communication is essential for safety during transport, handling, and emergencies.

In contrast, other options do not serve as the primary means of identifying the nature of the substance in the same direct way as the inscription. For example, a numerical code may reference specific regulations or categories but does not convey the substance’s actual hazards. A detailed description, while informative, is not the typical format for labeling; instead, it's often found in accompanying documentation. A pictogram might represent hazard classes visually, but it does not provide the specificity required for identifying the substance's nature like an inscription does.