Student A is correct. Hazardous waste can be solid, liquid, or gas. Option C is the right choice.
Hazardous waste can indeed take the form of solids, liquids, or gases. Examples of solid hazardous waste include contaminated soil, batteries, and asbestos.
Liquid hazardous waste can include paint thinners, solvents, and used oil. Gaseous hazardous waste can include emissions from industrial facilities and volatile organic compounds (VOCs). So, student A is correct.
Student B is incorrect as their statement is too restrictive. While many hazardous wastes are solids, there are significant examples of hazardous waste that exist in liquid and gaseous forms.
Option C is the right choice.