What qualifies as hazardous waste (HW)?

Hazardous waste (HW) is specifically defined as any discarded material that can pose a substantial or potential hazard to human health or the environment when improperly managed. This includes a broad range of materials that may possess harmful characteristics, such as ignitability, corrosivity, reactivity, or toxicity. The correct choice highlights the essential nature of hazardous waste classification, which relies on the material's harmful potential rather than simply its status as unused or discarded.

The other options either misinterpret what constitutes hazardous waste or limit the classification to inappropriate criteria. For example, not all unused materials qualify as hazardous waste; some may be completely safe and non-hazardous. Similarly, while many materials can be recycled, not all recyclable materials are hazardous; recycling processes often exclude hazardous components to protect environmental integrity. Lastly, limiting hazardous waste classification to materials in liquid form is incorrect, as hazardous waste can also include solid and gaseous states, emphasizing the need for a comprehensive understanding of materials regardless of their physical state.