Half-life: how much is left

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A radioactive sample goes through 3 half-lives. What percent of it is left, Ari?

   12.5 %
2. 2.

   A radioactive sample goes through 4 half-lives. What percent of it is left, Bo?

   6.25 %
3. 3.

   A radioactive sample goes through 5 half-lives. What percent of it is left, Esme?

   3.125 %
5. 4.

   Using the bar, what fraction is left after 2 half-lives, Jun?

   • 1/2
   • 1/4
   • 0
6. 5.

   Using the bar, after how many half-lives is 12.5% left, Kira?

   Use the picture in question 4.

   • 12.5
   • 8
   • 3
7. 6.

   Using the bar, does halving ever bring the amount exactly to zero, Luz?

   Use the picture in question 4.

   • No: it keeps getting smaller
   • Yes: after 4 half-lives
   • Yes: after 2 half-lives
8. 7.

   What is a half-life, Milo?

   • The time for half to decay
   • The sample's age
   • Half the time for the whole sample
9. 8.

   A 100 g radioactive sample passes one half-life. How much is left, Pia?

   • 0 g
   • 50 g
   • 25 g
10. 9.

    Which isotope is used to date ancient wood, Tala?

    • Fluorine-18
    • Carbon-14
    • Technetium-99m
11. 10.

    Why does carbon-14 work for things that were once alive, Zee?

    • Carbon-14 stays the same forever
    • Rocks are made of carbon-14
    • Living things take in carbon-14