A substance that spontaneously releases ionizing radiation would be labeled hazard classification:

• A. 7
• B. 9
• C. 11
• D. 13

Answer: (A)

The concept being tested is how hazardous materials are classified for transport. Radioactivity is treated as a distinct hazard class, separate from flammables, corrosives, or other dangers. When a substance spontaneously releases ionizing radiation, it is considered radioactive, so it belongs to the hazard class designated for radioactivity. This classification signals responders to expect radiation, require shielding, and follow specific exposure limits and regulatory requirements.

The other numbers in the choices do not represent radioactivity. They correspond to different hazard categories (or, in some systems, are not used for radioactivity at all). So the correct classification is the one that specifically denotes radioactive materials, which is used to convey the appropriate safety precautions.