It is a hazardous waste characteristic which applies to materials that are normally unstable or explosive. They can cause explosions, toxic fumes, gases or vapours when mixed with water.

• A. Reactivity
• B. Toxicity
• C. Ignitability
• D. Corrosivity

Answer: (A)

The key idea is how unstable materials can react under certain conditions. Reactivity describes wastes that are normally unstable or explosive and can undergo dangerous reactions, including explosions or the release of toxic fumes, gases, or vapors, especially when they come into contact with water. That makes them dangerous even without adding other reagents and explains why water interaction can trigger hazardous outcomes. The other characteristics describe different hazards: toxicity is harm from exposure to the substance, ignitability is the potential to ignite, and corrosivity is the ability to corrode materials or cause skin burns. So when a waste can explode or emit hazardous gases upon mixing with water, it fits reactivity.