These emit ionizing radiation.

• A. Radioactive Materials (RAM)
• B. Light bulbs
• C. Water
• D. Plastic

Answer: (A)

The key idea is that ionizing radiation comes from unstable atomic nuclei that decay over time. Radioactive materials contain those unstable nuclei, so they emit ionizing radiation in the form of alpha, beta, or gamma radiation as they decay. Light bulbs, water, and plastic do not inherently emit ionizing radiation during normal use. Light bulbs generate visible light through electrical processes, while water and plastic do not produce radiation on their own (they could be contaminated, but that’s not emission). So the substance that emits ionizing radiation is radioactive materials.