A given radioactive sample is reduced frorm 20 g to 1.25 g in 40 days. Its half-life would be:
Correct answer: A. 10 days
- A. 10 days
- B. 8 days
- C. 5 days
- D. 6 days
Explanation
Initial mass = 40g Final mass = 1.25g Number of haalf lives = n Initial mass x (1 / 2)n = final mass (1 / 2)n = final mass / initial mass ==> 0.5n = 1.25 / 20 0.5n = 0.0625 ==> 0.54 = 0.0625 n = 4 Total number of days = 40 Half life = 40 / n ==> half life = 40 / 4 =10
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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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