20+ 30 MCQs on Decay of Isotopes

Here are 20 multiple-choice questions (MCQs) on the Decay of Isotopes, covering alpha, beta, and gamma decay, suitable for the CSIR NET Life Science examination. The correct answers are provided at the end.

Multiple-Choice Questions (MCQs)

1. What is the primary characteristic of alpha (α) decay?

a) Emission of an electron

b) Emission of a helium nucleus

c) Conversion of a proton into a neutron

d) Release of high-energy electromagnetic waves

2. In beta-minus (β⁻) decay, what happens inside the nucleus?

a) A neutron transforms into a proton and emits an electron

b) A proton transforms into a neutron and emits an electron

c) A neutron is absorbed by the nucleus

d) A proton combines with an electron to form a neutron

3. Gamma (γ) radiation consists of:

a) Electrons

b) Positrons

c) High-energy photons

d) Helium nuclei

4. Which of the following types of radioactive decay results in the highest penetration power?

a) Alpha decay

b) Beta decay

c) Gamma decay

d) Neutron emission

5. Which decay process results in an increase in atomic number?

a) Alpha decay

b) Beta-minus decay

c) Beta-plus decay

d) Gamma decay

6. During positron (β⁺) emission, what particle is ejected?

a) Electron

b) Proton

c) Neutron

d) Positron

7. What is the major consequence of gamma decay?

a) Change in mass number

b) Change in atomic number

c) No change in atomic number or mass number

d) Conversion of neutrons to protons

8. What is the daughter nucleus when Uranium-238 undergoes alpha decay?

a) Thorium-234

b) Uranium-235

c) Protactinium-234

d) Radium-226

9. Which of the following decay types does not result in a transmutation of elements?

a) Alpha decay

b) Beta decay

c) Gamma decay

d) Neutron emission

10. Which type of radiation is the least penetrating and can be stopped by a sheet of paper?

a) Alpha radiation

b) Beta radiation

c) Gamma radiation

d) X-rays

11. Which of the following is NOT true about beta decay?

a) It can increase or decrease the atomic number of an element

b) It involves the transformation of neutrons or protons

c) It always emits an electron

d) It results in a change of the element

12. In which form of decay does a nucleus emit an electron-like particle with a positive charge?

a) Alpha decay

b) Beta-minus decay

c) Beta-plus decay

d) Gamma decay

13. The decay of Carbon-14 to Nitrogen-14 is an example of:

a) Alpha decay

b) Beta-minus decay

c) Beta-plus decay

d) Gamma decay

14. In beta decay, the emitted electron or positron originates from:

a) The nucleus

b) The electron cloud

c) The neutron-proton interaction in the outer shell

d) The energy levels of an atom

15. The biological effects of radiation are most severe when exposed to:

a) Alpha radiation inside the body

b) Beta radiation from an external source

c) Gamma radiation from a distant source

d) Low-energy X-rays

16. Which of the following isotopes undergoes beta decay?

a) Uranium-238

b) Carbon-14

c) Radon-222

d) Polonium-210

17. What is the fundamental force responsible for beta decay?

a) Gravitational force

b) Electromagnetic force

c) Weak nuclear force

d) Strong nuclear force

18. The process in which an unstable nucleus captures an inner electron and undergoes transformation is called:

a) Alpha decay

b) Beta decay

c) Electron capture

d) Gamma decay

19. Which radiation type is used in medical imaging and cancer therapy?

a) Alpha

b) Beta

c) Gamma

d) Neutron

20. Which of the following correctly represents a balanced alpha decay equation for ²³⁸U?

a) ²³⁸U → ²³⁴Th + α

b) ²³⁸U → ²³⁸Th + β⁻

c) ²³⁸U → ²³⁴Pa + γ

d) ²³⁸U → ²³⁴U + α

Correct Answers:

1. b) Emission of a helium nucleus

2. a) A neutron transforms into a proton and emits an electron

3. c) High-energy photons

4. c) Gamma decay

5. b) Beta-minus decay

6. d) Positron

7. c) No change in atomic number or mass number

8. a) Thorium-234

9. c) Gamma decay

10. a) Alpha radiation

11. c) It always emits an electron

12. c) Beta-plus decay

13. b) Beta-minus decay

14. a) The nucleus

15. a) Alpha radiation inside the body

16. b) Carbon-14

17. c) Weak nuclear force

18. c) Electron capture

19. c) Gamma

20. a) ²³⁸U → ²³⁴Th + α

Here are 30 multiple-choice questions (MCQs) covering the Decay of Isotopes, ranging from basic to advanced levels, suitable for CSIR NET Life Science examination. The questions include alpha, beta, and gamma decay with relevant examples.

Basic Level MCQs (1-10)

1. Which of the following particles is emitted in alpha decay?

a) Electron

b) Proton

c) Helium nucleus

d) Neutron

Answer: c) Helium nucleus

2. Alpha particles are composed of:

a) 2 protons and 2 neutrons

b) 2 electrons and 2 protons

c) 2 protons and 4 neutrons

d) 1 proton and 1 neutron

Answer: a) 2 protons and 2 neutrons

3. Beta decay involves the conversion of:

a) Proton into a neutron

b) Neutron into a proton

c) Electron into a positron

d) Neutron into an electron

Answer: b) Neutron into a proton

4. In gamma decay, the nucleus releases:

a) A helium nucleus

b) High-energy photons

c) Neutrons

d) Protons

Answer: b) High-energy photons

5. Which of the following statements about alpha decay is true?

a) It increases the atomic number of an element.

b) It results in the emission of an electron.

c) It reduces the atomic number by 2 and mass number by 4.

d) It does not change the atomic number.

Answer: c) It reduces the atomic number by 2 and mass number by 4.

6. Beta decay results in:

a) A decrease in atomic number

b) An increase in atomic number

c) A decrease in mass number

d) No change in atomic number

Answer: b) An increase in atomic number

7. Gamma rays have:

a) No charge and no mass

b) A negative charge

c) A positive charge

d) A large mass

Answer: a) No charge and no mass

8. The isotope Uranium-238 undergoes alpha decay to form:

a) Thorium-234

b) Radon-222

c) Plutonium-239

d) Carbon-14

Answer: a) Thorium-234

9. Which of the following is an example of a beta emitter?

a) Radium-226

b) Carbon-14

c) Uranium-238

d) Polonium-210

Answer: b) Carbon-14

10. The primary difference between beta-minus (β⁻) and beta-plus (β⁺) decay is:

a) β⁻ decay emits an electron, whereas β⁺ decay emits a positron

b) β⁻ decay decreases the atomic number

c) β⁺ decay results in neutron loss

d) Both increase the atomic number

Answer: a) β⁻ decay emits an electron, whereas β⁺ decay emits a positron

Intermediate Level MCQs (11-20)

11. The half-life of an isotope is the time taken for:

a) Half of the sample to decay

b) The entire sample to decay

c) The energy of the nucleus to double

d) The isotope to lose its charge

Answer: a) Half of the sample to decay

12. If the half-life of C-14 is 5730 years, how much of a 100g sample remains after 2 half-lives?

a) 100g

b) 50g

c) 25g

d) 12.5g

Answer: c) 25g

13. Positron emission is observed in:

a) Alpha decay

b) Beta-minus decay

c) Beta-plus decay

d) Gamma decay

Answer: c) Beta-plus decay

14. Which of the following undergoes beta decay?

a) Lead-206

b) Iodine-131

c) Thorium-232

d) Radium-226

Answer: b) Iodine-131

15. Gamma rays are emitted when:

a) An electron is captured

b) A neutron is converted into a proton

c) The nucleus moves to a lower energy state

d) A proton decays into a neutron

Answer: c) The nucleus moves to a lower energy state

16. The decay of Radon-222 releases:

a) Beta particles

b) Alpha particles

c) Gamma rays

d) Positrons

Answer: b) Alpha particles

17. What is the atomic number of Thorium-234 after undergoing beta decay?

a) 88

b) 89

c) 90

d) 91

Answer: b) 89

18. In a beta-minus decay, the number of protons in the nucleus:

a) Decreases by 1

b) Increases by 1

c) Remains the same

d) Becomes zero

Answer: b) Increases by 1

19. Which radioactive decay mode does NOT change the atomic number?

a) Alpha decay

b) Beta decay

c) Gamma decay

d) Positron emission

Answer: c) Gamma decay

20. Which element is commonly used in PET (Positron Emission Tomography) scans?

a) Carbon-14

b) Fluorine-18

c) Uranium-238

d) Thorium-232

Answer: b) Fluorine-18

Advanced Level MCQs (21-30)

21. The relationship between decay constant (λ) and half-life (t₁/₂) is:

a) λ = ln(2) / t₁/₂

b) λ = t₁/₂ × ln(2)

c) λ = t₁/₂ / ln(2)

d) λ = e^(t₁/₂)

Answer: a) λ = ln(2) / t₁/₂

22. Which radiation type is most penetrating?

a) Alpha

b) Beta

c) Gamma

d) Neutron

Answer: c) Gamma

23. The isotope Uranium-235 undergoes decay via:

a) Alpha emission

b) Beta decay

c) Electron capture

d) Gamma decay

Answer: a) Alpha emission

24. Which isotope is commonly used in radioactive dating?

a) Carbon-14

b) Polonium-210

c) Uranium-235

d) Radon-222

Answer: a) Carbon-14

25. The Fajans rule is used to predict:

a) Alpha decay

b) Beta decay

c) Gamma decay

d) Electron capture

Answer: d) Electron capture

26. The decay of Strontium-90 releases:

a) Alpha particles

b) Beta particles

c) Gamma rays

d) Neutrons

Answer: b) Beta particles

27. The SI unit of radioactive decay is:

a) Curie

b) Becquerel

c) Rutherford

d) Gray

Answer: b) Becquerel

28. In nuclear equations, the sum of mass numbers and atomic numbers on both sides must be:

a) Equal

b) Different

c) Zero

d) Random

Answer: a) Equal

29. The decay of Potassium-40 is an example of:

a) Alpha decay

b) Beta decay

c) Gamma decay

d) Fission

Answer: b) Beta decay

30. Which of the following has the shortest half-life?

a) Carbon-14

b) Polonium-210

c) Uranium-238

d) Thorium-232

Answer: b) Polonium-210