UPSC Prelims 2001 Q117: Science & Technology – Chemistry - Radioactivity
Which one of the following is NOT radioactive?
- (a) Astatine
- (b) Francium
- (c) Tritium
- (d) Zirconium
Answer: (d) Zirconium
Explanation
Element that is NOT radioactive
| Element | Radioactive? |
|---|---|
| Astatine (At, 85) | Yes — all isotopes radioactive; rarest natural element |
| Francium (Fr, 87) | Yes — all isotopes radioactive |
| Tritium (³H) | Yes — radioactive isotope of hydrogen, half-life about 12.3 years |
| Zirconium (Zr, 40) | No — its common isotopes are stable; used in reactor fuel cladding |
Zirconium is a stable metal, used as zircaloy to clad nuclear fuel because it absorbs few neutrons. Astatine and francium have no stable isotopes, and tritium is the radioactive isotope of hydrogen.
Answer: (d) Zirconium.
Why each option is right or wrong
- (a) Incorrect. Astatine is radioactive.
- (b) Incorrect. Francium is radioactive.
- (c) Incorrect. Tritium is radioactive.
- (d) CORRECT. Zirconium is not radioactive.
Key point
All elements beyond lead (82) are radioactive; technetium (43) and promethium (61) are the lighter exceptions.
Remember
Zirconium is stable; At, Fr and tritium are radioactive.
Common mistakes
- Thinking zirconium is radioactive because it is used in reactors.
- Forgetting that tritium is radioactive.
- Not knowing astatine and francium are unstable.
Exam tip
Heavy elements beyond lead are radioactive; light metals like zirconium usually are not.
Sources
- NCERT Class XI — Chemistry, chapter 'Classification of Elements and Periodicity in Properties'
- Royal Society of Chemistry — Periodic Table: zirconium, astatine, francium