The half life of 22Na is 2.6 years. If X grams of this sodium isotope are initially present, how much is left after 13 years.
Correct answer: A. X/32
- A. X/32
- B. X/13
- C. X/8
- D. X/5
Explanation
Half life is 2.6 yearsInitially x grams of sodium isotope were present After 13 years which is 13/2.6 = 5 years Let the amount of sodium left is y gramPutting formulaN=N°(½)n Here y = x(½)5 y = x/32
This question appeared on the ETEA MDCAT 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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