Half Lives

The half life of iodine-131 is 8 days. What fraction of an iodine-131 sample will remain after 40 days?

• 1/2

• 1/64

• 1/5

• 1/32

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NGSS.HS-PS1-8

Which of the following statements is true?

• An unstable daughter isotope decays into a stable parent isotope.

• An unstable parent isotope decays into a stable daughter isotope.

• A stable daughter isotope decays into an unstable parent isotope.

• A stable parent isotope decays into an unstable daughter isotope.

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NGSS.HS-PS1-8

After the third half-life, how much of a radioactive sample is left?

• 1/2

• 1/3

• 1/16

• 1/8

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NGSS.HS-PS1-8

¹⁴₆C has a half life of 5730 years, how many years would it take the 4.0 g sample to decay to 0.25 g?

• 4 years

• 5730 years

• 22,920 years

• 28,650 years

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NGSS.HS-PS1-8

A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of strontium-90 is 28 years. In what year will only 0.625 grams of this strontium-90 remain?

• 1988

• 2016

• 2044

• 2072

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NGSS.HS-PS1-8

A radioactive substance has a half-life of 10 years. If you start with 100 grams of the substance, how much will remain after 30 years?

• 25 grams

• 12.5 grams

• 50 grams

• 75 grams

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NGSS.HS-PS1-8

The half-life of a radioactive isotope is 5 days. If you start with 200 grams of the isotope, how much will remain after 15 days?

• 25 grams

• 100 grams

• 50 grams

• 75 grams

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NGSS.HS-PS1-8

A radioactive substance has a half-life of 2 hours. If you start with 500 grams of the substance, how much will remain after 6 hours?

• 125 grams

• 250 grams

• 375 grams

• 62.5 grams

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NGSS.HS-PS1-8

The half-life of a radioactive isotope is 1 year. If you start with 1000 grams of the isotope, how much will remain after 3 years?

• 125 grams

• 250 grams

• 500 grams

• 750 grams

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NGSS.HS-PS1-8

A radioactive substance has a half-life of 20 minutes. If you start with 800 grams of the substance, how much will remain after 1 hour?

• 600

• 400

• 100

• 200