Which material will form unstable peroxides upon reaction with atmospheric oxygen?

• A. Oxidizer
• B. Pyrophoric
• C. Disproportionation
• D. Peroxide Forming

Answer: (D)

Peroxide-forming materials are substances that, when exposed to atmospheric oxygen, can generate organic peroxides. Those peroxides can be unstable and even explosive, especially if the material has aged, is concentrated, or is heated or disturbed. That hazard—formation of unstable peroxides upon contact with air—is the reason this option is the best choice.

Other terms describe different hazards: an oxidizer is a substance that can promote oxidation and fuel fires but doesn’t specifically denote forming peroxides from air; pyrophoric materials ignite spontaneously in air rather than forming peroxides; disproportionation is a reaction type where a single species is converted into two species with different oxidation states, not a material's tendency to form peroxides; so they don’t capture the specific hazard described.