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GK QUESTION#3069

A radioactive substance has a half-life of 10 days. How long will it take for 75% of the original sample to decay?

  1. A15 days
  2. B12 days
  3. C20 daysCorrect answer
  4. D25 days
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Answer

C. 20 days

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Explanation

After one half-life, one-half of the original radioactive nuclei remain. After two, one-quarter remain, so three-quarters have decayed. With a 10-day half-life, the required time is 2 × 10 = 20 days.

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