Which statement about the hazardous materials inquiry is TRUE?

The statement regarding the hazardous materials inquiry being based on a fourteen-digit ultra number is accurate because this specific number is essential for identifying hazardous materials during transportation. The ultra number provides critical information necessary for maintaining safety and regulatory compliance in handling and transporting such materials, as it allows for detailed tracking and accountability.

In the context of hazardous materials regulations, the use of a fourteen-digit ultra number ensures that all pertinent data—such as the type of material, its handling requirements, and associated risks—can be easily accessed by authorities during an inquiry. This system helps in safeguarding public health and safety while also streamlining the process of managing hazardous materials across different transport modes.

The other choices do not align with the established protocols for hazardous materials inquiries. For instance, the six-digit code is not used in this context, the inquiry is not based solely on license plate numbers, and participation in hazardous materials inquiries is a requirement for commercial drivers, not an optional choice.