# Physics MCQs for Class 12 with Answers Chapter 13 Nuclei

### CBSE Class 12 Physics MCQs Solution All Chapters

Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 1 Electric Charges and Fields. 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 Electric Charges and Fields MCQs Pdf with Answers to know their preparation level.

### Nuclei Class 12 Physics MCQs

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.

Explaination:

### Nuclei Class 12 MCQs Questions with Answers

Question 1.
Beta rays emitted by a radioactive material are
(a) neutral particles.
(b) charged particles emitted by nucleus.
(d) electrons orbiting around the nucleus.

Answer: (b) charged particles emitted by nucleus.

Question 2
How much energy will approximately be released if all the atoms of 1 kg of deuterium could undergo fusion?
(a) 2 × 107 kWh
(b) 9 × 1013J
(c) 6 × 1027 Cal
(d) 8 × 1023 MeV.

Question 3.
The packing fraction for $$_{7}^{14}$$N isotope whose mass is 14.003 amu is:
(a) 0.9
(b) 7.8 × 10-3
(c) 1.0002
(d) 2.1 × 10-4

Question 4.
The binding energy per nucleon is almost constant for many nuclei. It shows that nuclear forces are
(a) Charge independent
(b) saturated in nature
(c) short range in nature
(d) attractive in nature

Question 5.
The binding energies per nucleon for a deutron and an α- particle are x1 and x2 respectively. The energy Q released in reaction
1H² + 1H² → $$_{2}^{4}$$He + Q is
(a) 4 (x1 + x2)
(b) 4 (x1 – x2)
(c) 2 (x1 + x2)
(d) 2 (X1 – x2).

Answer: (b) 4 (x1 – x2)

Question 6.
The binding energies of the atoms of elements A and B are Ea and Eb respectively. Three atoms of the elements B fuse to give one atom of element A. This fusion process is accompained by release of energy E. Then Ea, Eb and E are related to each other as:
(a) Ea + E = 3 Eb
(b) Ea = 3Eb
(c) Ea – E = 3 Eb
(d) Ea + 3Eb + E = 0

Answer: (a) Ea + E = 3 Eb

Question 7.
Let mn and mp be the masses of a neutron and a proton respectively. M1 and M2 are the masses of a $$_{10}^{20}$$Ne nucleus and a $$_{20}^{40}$$Ca nucleus respectively. Then
(a) M2 < 2M1
(b) M2 > 2M1
(c) M2 = 2M1
(d) M1 < 10 (mn + mp).

Question 8.
One requires an energy En to remove a nucleon from a nucleus and an energy Ee to remove an electron from an atom. Then
(a) En = Ee
(b) En > Ee
(c) En < Ee
(d) En > Ee.

Question 9.
When the number of nucleons in nuclei increases, the binding energy per nucleon numerically
(a) increases continuously with mass number.
(b) decreases continuously with mass number.
(c) First increases and then decreases with increase of mass number.
(d) Remains constant with mass number.

Answer: (c) First increases and then decreases with increase of mass number.

Question 10.
For an atomic reactor being critical, the ratio (k) of the average number of neutrons produced and used in chain reaction
(a) depends upon the mass of the fissionable material.
(b) is greater than one.
(c) is less than one.
(d) is equal to one.

Answer: (a) depends upon the mass of the fissionable material.

Question 11.
Maximum permissible radiation dose a a person may have with no adverse effects is
(a) 250 × 10-1 roentgen’s per week.
(b) 250 × 10-2 roentgen’s per week.
(c) 250 × 10-3 roentgen’s per week.
(d) 250 roentgen’s per week.

Answer: (c) 250 × 10-3 roentgen’s per week.

Question 12.
For thorium A = 232 and Z = 90. At the end of some radioactive disintegrations we obtain an isotope of lead with $$_{82}^{208}$$pb. Then the number of emitted α and ß particles are
(a) α = 4, ß = 6
(b) α = 5, ß = 5
(c) α = 6, ß = 4
(d) α = 6, ß = 6

Answer: (c) α = 6, ß = 4

Question 13.
If 10 % of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is nearly.
(a) 60%
(c) 75%
(b) 70%
(d) 66%

Question 14.
If the atomic masses for the parent and daughter element in a radioactive decay are Mp and Md and the mass of the electron me then the Q-value for the radioactive ß decay is given by
(a) Q = Mp
(b) Q = (Mp – Md – Mc) C²
(c) Q = (Mp – Md)C²
(d) Q = (Mp – md – 2Me)C².

Answer: (c) Q = (Mp – Md)C²

Question 15.
For the fission of heavy nucleus, neutron is more effective than the proton or a particle because
(a) Neutron is heavier than α-particle.
(b) Neutron is lighter than α-particle.
(c) Neutron moves with a small velocity.
(d) Neutron is uncharged.

Question 16.
Which of the following is the best nuclear fuel.
(a) Thorium-236
(b) Plutonium – 239
(c) Neptunium-239
(d) Uranium-236.

Question 17.
The energy released in the fission of a single $$_{92}^{235}$$U nucleus is 200 MeV. The fission rate of $$_{92}^{235}$$U fuelled reactor operating a power level of 5 Watt is
(a) 1.56 × 1014 per sec.
(b) 1.56 × 1017 per sec.
(c) 1.56 × 1020 per sec.
(d) 1.56 × 1017 per sec

Answer: (b) 1.56 × 1017 per sec.

Question 18.
Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is to
(a) absorb neutrons and stop chain reaction
(b) To cool the reactor
(c) To slow down the neutrons to thermal energies.
(d) To control the energy released.

Answer: (c) To slow down the neutrons to thermal energies.

Question 19.
The volume of a nucleus is smaller than that of an atom by a factor of:
(a) 10
(b) 105
(c) 1015
(d) 1010

Question 20.
Consider the fission reaction :
$$_{96}^{236}$$U → x117 + Y117 + 0n1 + 0n1
i.e., two nuclei of same mass numbers 117 are formed plus two neutrons. The binding energy per nuclear of X and Y is 8.5 MeV whereas U236 is 7.6 MeV. The total energy liberated will be about:
(a) 2 MeV
(b) 20 MeV
(c) 2,000 MeV
(d) 200 MeV

Question 21.
Fusion reations place at high temp, because
(a) Kinetic energy is high enough to overcome repulsion between nuclei.
(b) Nuclei break up at high temperature.
(c) Atoms are ionised at high temperature.
(d) Molecules break up at high temperature.

Answer: (a) Kinetic energy is high enough to overcome repulsion between nuclei.

Question 22.
Which of the following nuclei is most stable
(a) even-even
(b) odd-odd
(c) odd-even
(d) even-odd

Fill in the Blanks

Question 1.
Atoms having the same ……………….. but different ……………….. are called isotopes.

Question 2.
The size of the nucleus varies as ……………….. power of mass number.

Answer: ($$\frac {1}{3}$$)

Question 3
……………….. is the process in which light nuclei fuse together to form a heavy nucleus.

Question 4.
In the fission of 235U nucleus on an average ……………….. neutrons are released.

Question 5.
In a nuclear reactor, heavy water is used as a ……………….. which slows down the neutrons.

Question 6.
The difference between $$_{92}^{235}$$U and $$_{92}^{238}$$U is that $$_{92}^{238}$$U contains three more ……………….. and fission of $$_{92}^{238}$$U is caused ……………….. by neutrons while fission of $$_{92}^{235}$$U is caused by ……………….. neutrons.

Question 7.
The order of magnitude of the density of nuclear matter is ………………..

Question 8.
The average binding energy per nucleon for the nuclei lying in the middle of periodic table is nearly ………………..

Question 9.
Two deuterium nuclei can combine to form a ……………….. if they possess sufficiently

Answer: Helium nucleus, high kinetic energy.

Question 10.
The average energy released per fission of $$_{92}^{235}$$U is approximately ……………….. MeV.

Question 11.
Proton was discovered by ……………….. and neutron was discovered by ………………..

Question 12.
The ratio of the radii of the nuclei 13Al27 and 52Te125 is approximately ………………..

Question 13
……………….. was the fissionable material used in the bomb dropped at Nagasaki in 1945.

Question 14.
An element A decays into element C by a two step process:
A → B + $$_{2}^{4}$$He
B → C + 2e,
Then A and C are ………………..

Question 15.
The sun obtains its radiant energy from ………………..

Question 16.
The B.E. per nucleon is maximum for ………………..

Answer: $$_{26}^{56}$$Fe.

Question 17.
Slow neutrons are incident on a sample of uranium containing both $$_{92}^{235}$$U and $$_{92}^{238}$$U isotopes, then only ……………….. atoms will undergo fission. .

Answer: $$_{92}^{235}$$U

Question 18.
The critical mass of the fissionable material is ………………..

Answer: The minimum mass needed for chain reaction.

Question 19.
The bulk of energy released in nuclear fission process appears as ………………..

Answer: Kinetic energy of fission fragments.

Question 20.
In a given reascion:
$$_{Z}^{A}$$X → $$_{Z+1}^{A}$$Y → $$_{Z-1}^{A-4}$$K → $$_{Z-1}^{A-4}$$K

Question 21.
A positron has the same mass as ………………..

Question 22.
Neutrino is a particle with ………………..