1.

Lead-199 has a half-life of 1.5 hours. If a researcher begins with 2 grams of lead-199, how much will remain after 6 hours?

Answer»

0.125 grams
0.25 grams
0.375 grams
0.5 grams

Solution :Because each half-life is 1.5 HOURS, a time internval of 6 hours is EQUAL to 4 half-lives. After each half-life elapses, the MASS of the sample is cut in half, so after 4 half-lives, the mass of the sample decreases from 2 grams to 1gram to 0.5 grams to 0.25 grams and , FINALLY to 0.125 grams.


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