Half-life of a radioactive isotope is 5 years. What percentage remains after 15 years? MCQ with Answer and Explanation

Half-life of a radioactive isotope is 5 years. What percentage remains after 15 years?
A. 12.5%
B. 6.25%
C. 50%
D. 25%
Answer: Option A
Solution (By JKSSB Mock Tests)
15/5 = 3 half-lives. Remaining = (1/2)³ = 1/8 = 12.5%. Each half-life reduces the amount by half.

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