The correct answer is B) Poison gases. In accordance with U.S. regulations, a Class 2.3 substance is classified as a "Poison gas". This is based on the Hazardous Materials Regulations (HMR) set forth by the U.S. Department of Transportation, which categorize hazardous materials into different classes. Class 2.3 materials are specifically defined as "Toxic gases" or "Poison gases" that are known to be toxic to humans. The other answer choices are incorrect because they do not accurately describe the proper label name for a Class 2.3 substance. Flammable gases (A), non-flammable gases (C), and inert gases (D) are different hazard classes that do not apply to poison or toxic gases.