Half Life MCQs

21. The half-life of Radon-222 is approximately 3.8 days. How long will it take for 1/4 of the original amount to remain?

• A) 7.6 days
• B) 11.4 days
• C) 3.8 days
• D) 15.2 days
• Answer: A

22. A sample with a half-life of 20 minutes will have what fraction remaining after 60 minutes?

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

23. After 2 half-lives, the amount of radioactive substance left is:

• A) 1/2
• B) 1/3
• C) 1/4
• D) 1/8
• Answer: C

24. The half-life of Uranium-238 is:

• A) 4.5 million years
• B) 5730 years
• C) 4.5 billion years
• D) 100,000 years
• Answer: C

25. The decay constant (λ) is related to half-life (T₁/₂) by which of the following equations?

• A) T₁/₂ = ln(2) / λ
• B) T₁/₂ = λ / ln(2)
• C) T₁/₂ = 1 / λ
• D) T₁/₂ = λ² / ln(2)
• Answer: A

26. Which of the following substances has the longest half-life?

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

27. A substance has a half-life of 10 days. If you start with 80 grams, how much will remain after 30 days?

• A) 40 grams
• B) 20 grams
• C) 10 grams
• D) 5 grams
• Answer: D

28. After how many half-lives will only 1/16th of the original sample remain?

• A) 2
• B) 3
• C) 4
• D) 5
• Answer: C

29. The concept of half-life is crucial in:

• A) Thermodynamics
• B) Radioactivity
• C) Electrochemistry
• D) Optics
• Answer: B

30. Which of the following best explains why half-life is useful in radiocarbon dating?

• A) It helps in determining the current mass of a substance
• B) It allows for the calculation of the age of fossils and artifacts
• C) It determines the energy released during decay
• D) It is used to measure the temperature of substances
• Answer: B