Understanding Radioactive Decay Concepts

A sample of radioactive isotope has a half-life of 10 years. If you start with 80 grams, how much will remain after 20 years?

• 80 grams

• 40 grams

• 20 grams

• 10 grams

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NGSS.HS-PS1-8

Which of the following best describes what happens to the number of parent atoms during radioactive decay?

• The number of parent atoms increases over time.

• The number of parent atoms stays the same.

• The number of parent atoms decreases over time.

• The number of parent atoms disappears instantly.

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NGSS.HS-PS1-8

If a rock originally contained 100 grams of a radioactive isotope and now contains 25 grams, how many half-lives have passed?

• 1

• 2

• 3

• 4

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NGSS.HS-PS1-8

A scientist finds a fossil with 12.5% of its original radioactive isotope remaining. How many half-lives have passed since the organism died?

• 1

• 2

• 3

• 4

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NGSS.HS-PS1-8

Which statement correctly explains why radioactive decay is useful for determining the age of rocks?

• The rate of decay is constant and predictable.

• The rate of decay changes with temperature.

• The rate of decay depends on the rock’s location.

• The rate of decay can be controlled by scientists.

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NGSS.HS-PS1-8

If the half-life of a radioactive element is 5,000 years, how much of a 200-gram sample will remain after 15,000 years?

• 100 grams

• 50 grams

• 25 grams

• 12.5 grams

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NGSS.HS-PS1-8

A mineral sample contains equal amounts of a radioactive parent isotope and its stable daughter product. What can you conclude about the sample?

• No half-lives have passed.

• One half-life has passed.

• Two half-lives have passed.

• Three half-lives have passed.

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NGSS.HS-PS1-8

If a radioactive isotope has a half-life of 3 years, how long will it take for a sample to decay to 1/8 of its original amount?

• 3 years

• 6 years

• 9 years

• 12 years

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NGSS.HS-PS1-8

A geologist finds a rock with 6.25% of its original radioactive isotope remaining. How many half-lives have passed?

• 2

• 3

• 4

• 5

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NGSS.HS-PS1-8

Which of the following best explains why carbon-14 dating is not useful for dating rocks that are millions of years old?

• Carbon-14 decays too slowly.

• Carbon-14 decays too quickly.

• Carbon-14 is only found in living things.

• Carbon-14 is not radioactive.