Activity of a radioactive sample decreases to (1/3)rd of its original value in 3 days. Then in 9 days its activity will become (a) (1/27) of the original value (b) (1/9) of the original value (c) (1/18) of the original value (d) (1/3) of the original value

Answer: (a). Activity falls by the same factor in equal time intervals: factor 1/3 every 3 days. 9 days = 3 such intervals: A/A₀ = (1/3)³ = 1/27. So the answer is (a) 1/27 of the original value.

Activity of a radioactive sample decreases to (1/3)rd of its original… | MHT CET 2026 (14 May, Shift 1)

Q2MHT CET 2026 · 14 MAY · SHIFT 1Easy

Law of Radioactive Decay

Activity of a radioactive sample decreases to $\left(\frac{1}{3}\right)^{rd}$ of its original value in $3$ days. Then in $9$ days its activity will become

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Answer: (a)

Activity falls by the same factor in equal time intervals: factor $\frac{1}{3}$ every 3 days.
9 days = 3 such intervals: $\frac{A}{A_0} = \left(\frac{1}{3}\right)^3 = \frac{1}{27}$ .
So the answer is (a) $\frac{1}{27}$ of the original value.

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