41. **The half-life of Cobalt-60

is approximately 5 years. How much of a 100 gram sample will remain after 15 years?**

• A) 50 grams
• B) 25 grams
• C) 12.5 grams
• D) 6.25 grams
• Answer: C

42. A radioactive isotope decays to 1/64th of its original amount after 30 days. What is the half-life of the isotope?

• A) 10 days
• B) 5 days
• C) 15 days
• D) 2 days
• Answer: A

43. How is half-life related to the stability of a nucleus?

• A) A longer half-life means a more stable nucleus
• B) A shorter half-life means a more stable nucleus
• C) Half-life and stability are unrelated
• D) Stability is determined by external factors, not half-life
• Answer: A

44. Which of the following units is commonly used to measure half-life?

• A) Seconds
• B) Minutes
• C) Days
• D) All of the above
• Answer: D

45. After 5 half-lives, what fraction of the original radioactive sample remains?

• A) 1/32
• B) 1/16
• C) 1/64
• D) 1/8
• Answer: A

46. If a radioactive substance has a half-life of 1 day, how much of a 100 gram sample will remain after 3 days?

• A) 25 grams
• B) 50 grams
• C) 12.5 grams
• D) 6.25 grams
• Answer: C

47. Which of the following isotopes has a half-life useful for geological dating?

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

48. What is the half-life of a substance if 25% of it remains after 8 years?

• A) 8 years
• B) 4 years
• C) 2 years
• D) 16 years
• Answer: B

49. The half-life of Thorium-232 is:

• A) 14 billion years
• B) 1 billion years
• C) 100 million years
• D) 5730 years
• Answer: A

50. After one half-life, how much of a radioactive isotope remains undecayed?

• A) 100%
• B) 50%
• C) 25%
• D) 0%
• Answer: B