Half Life MCQs

31. A radioactive sample decays to 1/32 of its original amount after 25 years. What is the half-life of the substance?

• A) 5 years
• B) 10 years
• C) 15 years
• D) 25 years
• Answer: A

32. If a sample has a half-life of 12 hours, how long will it take for 75% of the sample to decay?

• A) 12 hours
• B) 24 hours
• C) 6 hours
• D) 36 hours
• Answer: B

33. What happens to a radioactive sample after one half-life?

• A) The sample completely decays
• B) Half of the atoms decay
• C) The sample’s mass is halved
• D) The sample stops emitting radiation
• Answer: B

34. The half-life of a substance is:

• A) The same for all elements
• B) Dependent on the external environment
• C) Unique for each radioactive isotope
• D) Constant, but only under certain temperatures
• Answer: C

35. If 100 grams of a radioactive isotope with a half-life of 5 years is present, how much will remain after 10 years?

• A) 50 grams
• B) 25 grams
• C) 10 grams
• D) 75 grams
• Answer: B

36. A shorter half-life means that a radioactive material will:

• A) Decay more slowly
• B) Be more stable
• C) Decay more quickly
• D) Have a lower energy release
• Answer: C

37. Which radioactive substance has a half-life useful for medical treatments such as cancer therapy?

• A) Iodine-131
• B) Carbon-14
• C) Uranium-238
• D) Radon-222
• Answer: A

38. Which of the following is true about half-life and activity of a radioactive sample?

• A) As half-life decreases, activity decreases
• B) As half-life decreases, activity increases
• C) Half-life has no effect on activity
• D) Half-life and activity are unrelated
• Answer: B

39. If a sample with a half-life of 1 hour starts with 200 grams, how much will remain after 3 hours?

• A) 100 grams
• B) 50 grams
• C) 25 grams
• D) 12.5 grams
• Answer: D

40. What percentage of a radioactive sample remains after 4 half-lives?

• A) 25%
• B) 12.5%
• C) 6.25%
• D) 3.125%
• Answer: C