The half life of a radioactive substance is T. The time taken, for disintegrating 7/8 th part of its original mass will be: (a) 8T (b) 3T (c) T (d) 2T

Answer: (b). If 7/8 disintegrates, 1/8 = (1/2)³ remains. So 3 half-lives: t = 3T. So the answer is (b) 3T.

The half life of a radioactive substance is T. The time taken, for… | JEE Main 2023 (10 Apr, Shift 2)

Q29JEE Main 2023 · 10 APR · SHIFT 2Easy

Law of Radioactive Decay

The half life of a radioactive substance is T. The time taken, for disintegrating $\frac{7}{8}$ th part of its original mass will be:

Show answer and solution

Answer: (b)

If $\frac{7}{8}$ disintegrates, $\frac{1}{8} = \left(\frac{1}{2}\right)^3$ remains.
So 3 half-lives: $t = 3T$ .
So the answer is (b) 3T.

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