Answer
5 mg
Work Step by Step
t= 24 hours+6 hours= 30 hours=2 half-lives.
After one half-life $\frac{1}{2}\times20\,mg$ remains.
After two half-lives $\frac{1}{2}\times\frac{1}{2}\times20\,mg$ remains. That is, 5 mg remains.
Chemistry: The Molecular Science (5th Edition)
by Moore, John W.; Stanitski, Conrad L.
Published by
Cengage Learning
ISBN 10:
1285199049
ISBN 13:
978-1-28519-904-7
Chapter 18 - Nuclear Chemistry - Questions for Review and Thought - Topical Questions - Page 817b: 28
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