The half-life of a radioactive substance is 5 years. The fraction disintegrated after 15 years is MCQ with Answer and Explanation

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The half-life of a radioactive substance is 5 years. The fraction disintegrated after 15 years is

A. 1/3

B. 1/8

C. 1/2

D. 7/8

Answer: Option D

Solution (By JKSSB Mock Tests)

After 3 half-lives, remaining = (1/2)³ = 1/8, so disintegrated = 1 - 1/8 = 7/8. Fraction disintegrated = 7/8. Option A remaining. So B.

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