11. Half-life refers to:

• A) The time taken for a radioactive sample to become completely stable
• B) The time taken for half the atoms in a radioactive sample to decay
• C) The time taken for the total mass of a substance to decrease by half
• D) The time taken for the volume of a substance to reduce by half
• Answer: B

12. If a substance has a half-life of 5 years, what fraction of the original sample remains after 15 years?

• A) 1/8
• B) 1/4
• C) 1/2
• D) 1/16
• Answer: A

13. The half-life of a radioactive isotope depends on:

• A) Temperature
• B) Pressure
• C) The initial quantity of the isotope
• D) The nature of the isotope
• Answer: D

14. Which of the following isotopes has a half-life of approximately 5730 years?

• A) Uranium-238
• B) Carbon-14
• C) Thorium-232
• D) Potassium-40
• Answer: B

15. The half-life of a radioactive element is 10 minutes. How much of the original sample remains after 30 minutes?

• A) 1/4
• B) 1/8
• C) 1/16
• D) 1/2
• Answer: B

16. Which of the following best describes half-life?

• A) It is the time taken for the nucleus of an atom to split
• B) It is the time required for half the nuclei in a sample to decay
• C) It is the time needed for an atom to form
• D) It is the time taken for half the energy of a particle to dissipate
• Answer: B

17. The shorter the half-life of a radioactive substance, the:

• A) Slower the rate of decay
• B) Faster the rate of decay
• C) Lower the energy released
• D) More stable the substance
• Answer: B

18. If the half-life of a substance is 8 hours, how much of the original substance remains after 24 hours?

• A) 1/4
• B) 1/8
• C) 1/2
• D) 1/16
• Answer: B

19. For a substance with a half-life of 6 years, what fraction of the sample remains after 18 years?

• A) 1/3
• B) 1/8
• C) 1/6
• D) 1/16
• Answer: B

20. Which of the following statements is true about half-life?

• A) It is constant for a given isotope
• B) It varies depending on the amount of the isotope
• C) It depends on the temperature
• D) It increases over time
• Answer: A