A radioactive substance has a half-life of four months, three-fourth of the substance will decay in:
Correct answer: C. 8 months
- A. 3 months
- B. 4 months
- C. 8 months
- D. 12 months
Explanation
t1/2 = 4 months Amount of substance left: 1 - 3 / 4 = 0.25 Number of half lives=n (1 / 2)n = amount of substance left (1 / 2)n = 0.25 ==> 0.5n = 0.25 0.52 = 0.25 n = 2 Total time for amount to reduce by 3 / 4 = 4 x 2 = 8 months .
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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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