Technetium-99m, an important radionuclide in medicine, has a half-life of 6.0 hours. What percentage of a sample of technetium-99m will remain undecayed after each of the given times? .813 12.0 hours: Incorrect Answer 6.25 1 day: Correct Answer 5 half-lives: 3.13 Correct Answer % % %

Define the term half-life and illustrate it with an example.

A sample of rock was found to contain 8.23 mg of rubidium-87 and 0.47 mg of strontium-87.. (a) Calculate the age of the rock if the half-life of the decay of rubidium by emission is 4.71010 y. (b) If some S3887r was initially present in the rock, would the rock be younger, older, or the same age as the age calculated in (a)? Explain your answer.