The four-digit ID number on a placard or shipping paper is the:
Correct. The four-digit number is the UN/NA ID — used with the ERG to find emergency response procedures.
CDL Practice Question #262
Category: Hazmat
Why this question matters
This question is one of 68 in our Hazmat bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.