Technetium-99m, used in medical imaging procedures, has a half-life of 6.0 hours. If an 84 mg sample of Tc-99m is transported at 7:00 a.m., determine the amount of Tc-99m (in milligrams) that remains active when it arrives at its destination at 7:00 p.m.

A sample of Mo-99 has a half-life of 2.75 days. After 16.5 days, the activity of the sample was reduced to 378 Bq. Calculate the initial activity, in becquerels, of the sample.

Yttrium-90 has a half-life of 2.67 days. Determine the number of half-lives elapsed for a sample of Y-90 after 5.34 days.

In a chemical laboratory, a way to handle a chemical spill, such as a spill of a strong acid like HCl, is to neutralize it with a weak base like NaHCO₃. Explain why harmful radioactive wastes from nuclear plants cannot be cleaned up as easily as cleaning up chemical spills.

What does the following statement imply? "Thorium-232, a radioactive metal used in manufacturing lenses for scientific instruments, has a half-life of 1.4×10¹⁰ years."