Half-Life & Radioactive Decay

Multiple Choice

If Bromine has 35 protons and a mass of 80, how many neutrons does it have?

• 35

• 115

• 45

Multiple Choice

After 22,800 years, approximately what percentage of the original carbon-14 remains?

• 15%

• 12.5%

• 6.25%

• 3.125%

Multiple Choice

The diagram shows 32 atoms.

16 of the Red are parent isotopes

16 of the Green are daughter isotopes

How many half-lives have occurred?

• 0

• 1

• 2

• 3

Multiple Choice

Which diagram best represents the percentage of this radioactive isotope sample that will remain after 2 half-lives?

Multiple Choice

What is the half-life of iodine-131?

• 32 days
• 8 days
• 16 days
• 24 days

Multiple Choice

The % of the parent isotope remaining after 1 Half Life.

• 50%

• 25%

• 12.5%

• 6.25%

Multiple Choice

The % of the parent isotope remaining after 2 Half Lives.

• 50%

• 25%

• 12.5%

• 6.25%

Multiple Choice

What is the Half life of this isotope?

• 5 seconds

• 10 seconds

• 15 seconds

• 20 seconds

Multiple Choice

Half life (in radioactivity) is the amount of time it takes for half of a radioactive sample to

• split.

• combine.

• decay.

• become parent material.

Multiple Choice

If 20 mg of iodine-131 is given to a patient, how much is left after 32 days? The half-life of iodine-131 is 8 days.

• 32

• 1.25

• 10

• 2.5

Multiple Choice

Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?

• 0.25g

• 2.5g

• 25g

• 80g

Multiple Choice

If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8 days.

• 1.25mg
• 1.25g
• 10g
• 10mg

Multiple Choice

If the half-life of uranium-232 is 70 years, how many half-lives will it take for 10 g of it to be reduced to 1.25 g?

• 1 half-life
• 2 half-lives
• 3 half-lives
• 4 half-lives

Multiple Choice

Based on the information given, approximately how long would it take for 25 potassium atoms to decay starting with an original sample size of 100?

• 0.64 billion years

• 2.56 billion years

• 1.28 billion years

• 1.92 billion years

Multiple Choice

Uranium-235 decays into lead-207 with a half life of 704 million years.  A sample of granite (an igneous rock formed by the solidification of magma within the crust) was found that contains 12.5% uranium-235 and 87.5% lead-207.  How old is the granite rock?

• 2.1 billion years

• 704 million years

• 1.4 billion years

• 302 million years