Which characteristic indicates a waste that is reactive?

A waste is classified as reactive if it has the potential to undergo violent chemical reactions that can lead to explosions, the release of toxic gases, or generate heat under certain conditions. The characteristic of being reactive is specifically associated with materials that can react vigorously with water, air, or other substances, leading to hazardous scenarios.

In this context, the correct choice highlights the potential for a waste to explode or emit dangerous gases, which is a defining feature of reactive waste. This characteristic poses significant risks in terms of environmental safety and health risks to individuals who may come into contact with or manage these materials.

While the other options describe important concerns related to waste management—such as ignitability, corrosiveness, and toxicity when ingested—they do not encapsulate the specific reactive nature that is critical for classification under hazardous waste regulations. Therefore, the defining feature that aligns with the reactivity classification is the ability of a waste to explode or release toxic gases.