The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to ≤ft(1/16)^th of its initial value?

1. 80 minutes

2. 20 minutes

3. 40 minutes

4. 60 minutes

Doubtly Asked 30 Oct 2026 NEET UG 2023 neet Save WhatsApp Report

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Answer: 1. 80 minutes

Activity falls by half every half-life. \(\dfrac1{16}=\left(\dfrac12\right)^4\), so 4 half-lives are needed.

\(t=4\times20=80\) minutes. The answer is 80 minutes.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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