A certain radioactive isotope has a half-life of 50 days. Fraction of the material left behind after 100 days will be:
Correct answer: B. 25%
- A. 125%
- B. 25%
- C. 50%
- D. 100%
Explanation
50 days is one half life. So 100 days means 2 half lives.After every half life, the substance halves in amount.After the first half life, material will become 50% of the original material.After the second half life, material will become half of 50% ie 25%.100% → 50% → 25% 1 half live 2 half lifeHence, B is the answer.
This question appeared on the NUMS 2014 paper, which you can sit online with every answer explained.
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About Half-life and Rate of Decay
Half-life is the time required for half the unstable nuclei in a sample to decay, and it remains constant for a particular radioactive nuclide. Questions use the exponential decay law, decay constant, activity, remaining quantity and mean life. Radioactive decay is random for individual nuclei but predictable for large samples.
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