Which section of the Emergency Response Guidebook (ERG) lists chemicals by their UN identification numbers?

The section of the Emergency Response Guidebook (ERG) that lists chemicals by their UN identification numbers is indeed the Yellow section. This section is specifically designed to allow users to quickly find information on hazardous materials when they have the unique UN number, which is a consistent and reliable identifier for various substances. The Yellow section organizes materials in numerical order, making it easy for first responders to look up specific chemicals and determine the appropriate emergency response actions, which is critical for safety and effective handling of hazardous situations.

The Green section focuses on specific guidelines for evacuation distances, while the Blue section allows users to look up materials alphabetically by name. The Red section is related to specific alerts to guide responders through various emergency situations, but it does not provide a systematic way to locate chemicals based on their identification numbers. Thus, the Yellow section is the correct choice for finding chemicals by their UN numbers.