# Physics MCQs for Class 12 with Answers Chapter 13 Nuclei

Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 13 Nuclei. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. Students can solve NCERT Class 12 Physics Nuclei MCQs Pdf with Answers to know their preparation level.

## Nuclei Class 12 Physics MCQs Pdf

Atoms and Nuclei Class 12 MCQ Question 1. When a β-particle is emitted from a nucleus then its neutron-proton ratio
(a) increases
(b) decreases
(c) remains unchanged.
(d) may increase or decrease depending upon the nucleus.

Explaination:
(b) In P-decay neutron converts to proton with emission of electron and neutrino.

Physics MCQs with Answers for Class 12 Question 2. The relation between half-life T1/2 of a radioactive sample and its mean life x is Explaination: 3. The quantity which is not conserved in a nuclear reaction is
(a) momentum.
(b) charge.
(c) mass.
(d) none of these.

Explaination: (c) Energy equivalent to mass detect is released.

4. The half-life of a radioactive nucleus is 3 hours. In 9 hours, its activity will be reduced to a factor of CBSE Class 12 Physics MCQs with Answer: d
Explaination: MCQs Of Physics 2nd Year with Answers Chapter 13 Question 5. A radioactive element has half-life period 1600 years. After 6400 years what amount will remain? Explaination: Class 12 Physics MCQs Pdf Question 6. Ratio of the radii of the nuclei with mass numbers 8 and 27 would be Explaination: 7. A radioactive nucleus emits a beta particle. The parent and daughter nuclei are
(a) isotopes
(b) isotones
(c) isomers
(d) isobars

Explaination:
(d) Isobars have the same atomic mass but 1 different atomic number.

Physics MCQs for Class 11 Chapter wise Pdf Question 8. In the disintegration series the values of Z and A respectively will be
(a) 92, 236
(b) 88, 230
(c) 90, 234
(d) 91, 234

Explaination: CBSE Class 12 Physics MCQ Pdf Question 9. A nucleus $$_{Z}^{\mathbf{A}} \mathbf{X}$$ emits an α-particle. The resultant nucleus emits a β-particle. The respective atomic and mass numbers of the daughter nucleus will be
(a) Z – 3, A – 4
(b) Z – 1, A – 4
(c) Z – 2, A – 4
(d) Z, A – 2

Explaination: 10. In the nuclear reaction What does X stand for?
(a) Electron
(b) Proton
(c) Neutron
(d) Neutrino

Explaination:
(d) By conservation of mass A = 0, and by conservation of charge Z = 0, Hence X is neutrino.

11. The set which represent the isotope, isobar, and isotone respectively is 12. The mass number of iron nucleus is 56 the nuclear density is
(a) 2.29 × 1016 kg m-3
(b) 2.29 × 1017 kg m-3
(c) 2.29 × 1018 kg m-3
(d) 2.29 × 1015 kg m-3

13. Order of magnitude of density of uranium nucleus is
(a) 1020 kg m-3
(b) 1017 kg m-3
(c) 1014 kg m-3
(d) 1011 kg m-3

14. The radius of a spherical nucleus as measured by electron scattering is 3.6 fm. What is the mass number of the nucleus most likely to be?
(a) 27
(b) 40
(c) 56
(d) 120

15. The half life of a radioactive susbtance is 30 days. What is the time taken to disintegrate to 3/4th of its original mass?
(a) 30 days
(b) 15 days
(c) 60 days
(d) 90 days

16. The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an
(a) isomer of parent
(b) isotone of parent
(c) isotope of parent
(d) isobar of parent

17. During negative β-decay, an antineutrino is also emitted along with the emitted electron. Then,
(a) only linear momentum will be conserved
(b) total linear momentum and total angular momentum but not total energy will be conserved
(c) total linear momentum, and total energy but not total angular momentum will conserved
(d) total linear momentum, total angular momentum and total energy will be conserved

18. Consider α and β particles and γ-rays each having an energy of 0.5 MeV. In the increasing order of penetrating power, the radiation are respectively
(a) α, β, γ
(b) α, γ, β
(c) β, γ, α
(d) γ β, α

19. An electron emitted in beta radiation originates from
(a) inner orbits of atom
(b) free electrons existing in the nuclei
(c) decay of a neutron in a nuclei
(d) photon escaping from the nucleus

20. Complete the series 6He → e + 6Li +
(a) neutrino
(b) antineutrino
(c) proton
(d) neutron

21. An element A decays into an element C by a two step process A → B+ 2He4 and B → C + 2e. Then,
(a) A and C are isotopes
(b) A and C are isobars
(c) B and C are isotopes
(d) A and B are isobars

22. The equation 41 1H+ → 24He2+ + 2e + 26 MeV
represents
(a) β-decay
(b) γ-decay
(c) fusion
(d) fission

23. Light energy emitted by star is due to
(a) breaking of nuclei
(b) joining of nuclei
(c) burning of nuclei
(d) reflection of solar light

24. In nuclear reaction, there is conservation of
(a) mass only
(b) energy only
(c) momentum only
(d) mass, energy and momentum

25. In nuclear reactors, the control rods are made of
(b) graphite
(c) krypton
(d) plutonium

26. Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half-life of 1 year. After 1 year, [NCERT Exemplar]
(a) all the containers will have 5000 atoms of the material.
(b) all the containers will contain the same number of atoms of the material but that number will only be approximately 5000.
(c) the containers will in general have different numbers of the atoms of the material but their average will be close to 5000.
(d) none of the containers can have more than 5000 atoms.

27. Jhe gravitational force between a H-atom and another particle of mass m will be given by Newton’s law: [NCERT Exemplar] = magnitude of the potential energy of electron in the H-atom).

28. When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom [NCERT Exemplar]
(a) do not change for any type of radioactivity.
(c) change for α-radioactivity but not for others.
(d) change for β-radioactivity but not for others.

29. Mx and My denote the atomic masses of the parent and the daughter nuclei respectively in a radioactive decay. The Q-value for a β decay is Q1 and that for a β+ decay is Q2 If me denotes the mass of an electron, then which of the following statements is correct? [NCERT Exemplar] 30. Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into p + $$\bar{e}+\bar{v}$$. If one of the neutrons in Triton decays, it would transform into He3 nucleus. This does not happen. This is because [NCERT Exemplar]
(a) Triton energy is less than that of a He3\ nucleus.
(b) the electron created in the beta decay process cannot remain in the nucleus.
(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a He3 nucleus.
(d) because free neutrons decay due to external perturbations which is absent in a triton nucleus.

31. Heavy stable nuclei have more neutrons than protons. This is because of the fact that [NCERT Exemplar]
(a) neutrons are heavier than protons.
(b) electrostatic force between protons are repulsive.
(c) neutrons decay into protons through beta decay.
(d) nuclear forces between neutrons are weaker than that between protons.

32. Samples of two radioactive nuclides A and B are taken λA and λB are the disintegration constants of A and B respectively. In which of the following cases, the two samples can simultaneously have the same decay rate at any time?
(a) Initial rate of decay of A is twice the » initial rate of decay of B and λA = λB.
(b) Initial rate of decay of A is less than the initial rate of decay of B and λA < λB.
(c) Initial rate of decay of B is twice the initial rate of decay of A and λA > λB.
(d) Initial rate of decay of B is same as the rate of decay of A at t = 2h and λB = λA.

33. The variation of decay rate of two radioactive samples A and B with time is shown in figure. Which of the following statements are true? (a) Decay constant of A is greater than that of B, hence A always decays faster than B.
(b) Decay constant of B is greater than that of A but its decay rate is always smaller than that of A.
(c) Decay constant of A is equal to that ofB.
(d) Decay constant of B is smaller than that of A but still its decay rate becomes equal to that of A at a later instant.

34. Radioactivity is the phenomenon associated with
(a) decay of nucleus.

35. Which of the following are not emitted by radioactive substances?
(a) Electrons
(b) Protons
(c) Gamma rays
(d) Helium nuclei

36. In an α-decay
(a) the parent and daughter nuclei have some number of protons.
(b) the daughter nucleus has one proton more than parent nucleus.
(c) the daughter nucleus has two protons less than parent nucleus.
(d) the daughter nucleus has two nucleus more than parent nucleus.

37. When a radioactive nucleus emits a (β-particle, the mass number of the atom:
(a) increases by one.
(b) remains the same.
(c) decreases by one.
(d) decreases by four.

38. In a β-decay
(a) the parent and daughter nuclei have the same number of protons.
(b) the daughter nucleus has one proton less than parent nucleus.
(c) the daughter nucleus has one proton more than the parent nucleus.
(d) the daughter nucleus has one neutron more than the parent nucleus.

39. P-rays emitted by a radioactive material are
(b) electrons orbiting around the nucleus.
(c) neutral particles.
(d) charged particles emitted by nucleus.

40. During a mean life of a radioactive element the fraction that disintegrates is 41. γ-rays are originated from
(a) nucleus.
(b) outermost shell of nucleus.
(c) innermost shell of nucleus.
(d) outermost shell of atom.

42. Binding energy per nucleon of a stable nucleus is
(a) 8 eV
(b) 8 KeV
(c) 8 MeV
(d) 8 BeV

43. Sun’s radiant energy is due to
(a) nuclear fission.
(b) nuclear fusion.
(c) photoelectric effect.

44. Average binding energy is maximum for
(a) C12
(b) Fe56
(c) U235
(d) Po210

45. A nucleus undergoes γ-decay due to
(a) excess of protons.
(b) excess of neutrons.
(c) large mass.
(d) its excited state.

46. The decay constant of a radioactive substance is X. Its half-life and mean life, respectively are 47. Neutrino is a particle, which is chargeless and has spin.

Explaination: ±$$\frac{1}{2}$$

48. Isotones have the same number of _________ .

Explaination: neutrons

49. Packing fraction of a nucleus is its _________ its per nucleon.

Explaination: mass defect

50. How is the radius of a nucleus related to its mass number? [Panchkula 2019] [AI2011C]

Explaination:
The radius if of a nucleus of mass number A is related as if = R0A1/3, where R0 is a constant.

51. Two nuclei have mass numbers in the ratio 27 : 125. What is the ratio of their nuclear radii?

Explaination: 52. Two nuclei have mass numbers in the ratio 2 : 5. What is the ratio of their nuclear densities?

Explaination:
Nuclear density is independent of mass number. So, the ratio will be 1 : 1.

53. What is the relation between the binding energy per nucleon and stability of a nucleus?

Explaination:
The larger the binding energy per nucleon, the more stable is the nucleus.

54. Write any two characteristic properties of nuclear force. [Chennai-2019] [AI 2012,13]

Explaination:
The following are the two characteristic properties:
(i) Nuclear force is a short range force.
(ii) Nuclear forces show the saturation effect.

55. How is the mean life of a radioactive sample related to its half-life? [Foreign 2011]

Explaination: 56. Define the activity of a given radioactive substance. Write its SI unit.

Explaination:
The rate of disintegration or count rate of sample of radioactive material is called activity. The SI unit of activity is becquerel (Bq).

57. The radioactive isotope D decays according to the sequence If the mass number and atomic number of D2 are 176 and 71 respectively, what is
(i) the mass number
(ii) atomic number of D?

Explaination: (i) Mass number of D = 180
(ii) Atomic number of D = 72

58. A nucleus $$_{n} X^{m}$$ emits one a-particle and one β-particle. What is the mass number and atomic number of the product nucleus?

Explaination: Hence, the mass number of product is m – 4, and the atomic number of product is n – 1.

59. In both β and β+ decay processes, the mass number of a nucleus remains same, whereas the atomic number Z increases by one in β decay and decreases by one in β+ decay. Explain, giving reason. [Foreign 2014]

Explaination:
In β decay, one neutron inside the nucleus decays into one proton and one electron (β). The proton remains inside the nucleus and the electron is ejected out. In β+ decay, the conversion of proton into neutron and position (β+) takes place. 60. Which nucleus has greater mean life, A or B?

Explaination: Since, slope of A is more than slope of B.
Therefore, X is high and mean life e = $$\frac{1}{\lambda}$$ for A is small. 61. Why is a free neutron unstable but a free proton is a stable particle?

Explaination:
A free neutron is unstable outside the nucleus with an average life of 1000 s. It decays into a proton and emits a β particle, i.e. 62. A neutron strikes a nucleus of $$_{5}^{\mathbf{10}} \mathbf{B}$$ and emits an alpha particle. Write down the nuclear reaction for it.

Explaination: 63. Write the necessary condition required for fusion reaction.

Explaination:
(i) Nuclear fusion will occur when the kinetic energy of colliding nuclei is enough to overcome the strong electrostatic forces of repulsion between the protons. For this, high temperature is required.
(ii) The density of nuclei should also be very high to increase the number of collisions.

64. Out of $$_{14}^{30} X ;_{3}^{6} Y \text { and }_{40} Z^{130}$$, which is more likely to undergo the nuclear fusion?

Explaination:
A lighter unstable nucleus $$_{3}^{\mathbf{6}} \mathbf{Y}$$ can undergo the nuclear fusion.

65. What is the effect of temperature on radioactivity?

Explaination:
No effect. Radioactivity is independent of temperature.

66. What is the difference between an electron and a β-particle?

Explaination:
An electron resides outside the nucleus, whereas β-particle is an electron like particle of nuclear origin.

67. What is the source of stellar energy?

Explaination: Nuclear fusion reactions.

68. Four nuclei of an element fuse together to form a heavier nucleus. If the process is accompanied by the release of energy, which of the two—the parent or the daughter nucleus would have a higher binding energy/ nucleons? [CBSE 2018]

Explaination: Daughter nucleus.

69. You are given two nuelei $$_{3}^{7} X \text { and }_{3}^{4} Y$$, which one of the two is likely to be more stable? Give reason.

Explaination: $$_{3}^{\mathbf{7}} \mathbf{X}$$ is more stable, as it contains more neutrons than protons.
70. The $$_{10}^{\mathbf{23}} \mathbf{Ne}$$ decays by β emission into $$_{11}^{\mathbf{23}} \mathbf{Na}$$. Write down the β decay equation. 