Question:
Identify radioactive element from the following.
Identify radioactive element from the following.
Show Hint
Francium is the last member of group 1 and has no stable isotope.
Updated On: Nov 12, 2026
- \(\text{Fr}\)
- \(\text{K}\)
- \(\text{Rb}\)
- \(\text{Li}\)
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept
All the given elements are alkali metals of group 1.
Step 2: Identify the radioactive one
Lithium, potassium and rubidium have stable (or very long-lived) isotopes. Francium (\(Z=87\)) has only short-lived radioactive isotopes.
Step 3: Conclusion
The longest-lived isotope of francium has a half-life of only about 22 minutes, so francium is the radioactive element.
Final Answer:
Francium is the radioactive alkali metal. \[ \boxed{\text{(A) }\text{Fr}} \]
All the given elements are alkali metals of group 1.
Step 2: Identify the radioactive one
Lithium, potassium and rubidium have stable (or very long-lived) isotopes. Francium (\(Z=87\)) has only short-lived radioactive isotopes.
Step 3: Conclusion
The longest-lived isotope of francium has a half-life of only about 22 minutes, so francium is the radioactive element.
Final Answer:
Francium is the radioactive alkali metal. \[ \boxed{\text{(A) }\text{Fr}} \]
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