Which of the following is a physical toxic agent?

• A. Radiation
• B. Lead
• C. Bacteria
• D. Virus

Answer: (A)

The main idea is to recognize what counts as a physical toxic agent: toxicity caused by energy or physical forces rather than by a chemical substance or a living organism. Radiation fits this because it is a form of energy that can damage biology through physical interactions with cells and DNA—ionizing radiation can knock electrons off molecules, creating reactive species that damage cellular components, while non‑ionizing forms can cause harm mainly through heating or other energy effects. This is different from a chemical toxicant like lead, which exerts toxicity through chemical reactions and disturbance of biological processes, or from bacteria and viruses, which cause harm as living organisms (and may produce toxins, which are chemical, but the primary agent here is biological). So radiation is considered a physical toxic agent because its toxic effects arise from its physical energy interactions with matter, not from being a chemical substance or a living organism.