Which of the following is NOT one of the hazard class numbers under DOT regulations?

DOT hazard classes are numbered 1 through 9, with no Class 11. The full list: Class 1 — Explosives; Class 2 — Gases (2.1 flammable gas, 2.2 non-flammable non-toxic gas, 2.3 toxic gas); Class 3 — Flammable liquids; Class 4 — Flammable solids and self-reactive substances; Class 5 — Oxidizers and organic peroxides; Class 6 — Toxic substances (6.1) and infectious substances (6.2); Class 7 — Radioactive materials; Class 8 — Corrosive substances; Class 9 — Miscellaneous hazardous materials (anything dangerous that does not fit Classes 1-8, such as lithium batteries and elevated-temperature materials). Within most classes, divisions (2.1, 2.2, 6.1, etc.) further specify the type of hazard.