Final answer:
The substance 'Compressed gas, toxic, n.o.s. Inhalation Hazard Zone A' belongs to Hazard Class 2, specifically Division 2.3 for toxic gases. It's indicated by 'n.o.s.', which means not otherwise specified, and Inhalation Hazard Zone A represents a severe inhalation risk.
Step-by-step explanation:
The correct hazard class or division for a substance labeled as "Compressed gas, toxic, n.o.s. Inhalation Hazard Zone A" falls under Hazard Class 2, which specifically pertains to gases. Substances within this class are further divided based on their properties, such as being flammable (Division 2.1), non-flammable/non-toxic (Division 2.2), or toxic (Division 2.3). The "n.o.s." notation stands for "not otherwise specified," meaning that the gas isn't specified under a particular name within the regulations. Inhalation Hazard Zone A signifies that the gas poses a severe inhalation hazard to people, indicating it can be lethal even in small quantities or with short exposure durations.
The National Fire Protection Association (NFPA) 704 Hazard Identification System provides additional safety information. It uses a diamond-shaped symbol to indicate the level of fire hazard (red), health hazard (blue), reactivity (yellow), and special hazards (white), each rated on a scale from 0 to 4.