Physics MCQs for Class 12 with Answers Chapter 13 Nuclei

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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.

Answer/Explanation

Answer: b
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
Physics MCQ Questions For Class 12 Pdf Download

 
Answer/Explanation

Answer: a
Explaination:
Physics MCQ Questions for Class 12 Pdf


3. The quantity which is not conserved in a nuclear reaction is
(a) momentum.
(b) charge.
(c) mass.
(d) none of these.

Answer/Explanation

Answer: c
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
Physics MCQs for Class 12 Chapter wise with Answers Pdf

Answer/Explanation

CBSE Class 12 Physics MCQs with Answer: d
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 15


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?
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 8

Answer/Explanation

Answer: b
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 16


Class 12 Physics MCQs Pdf Question 6. Ratio of the radii of the nuclei with mass numbers 8 and 27 would be
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 9

Answer/Explanation

Answer: c
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 17


7. A radioactive nucleus emits a beta particle. The parent and daughter nuclei are
(a) isotopes
(b) isotones
(c) isomers
(d) isobars

Answer/Explanation

Answer: d
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
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 11
the values of Z and A respectively will be
(a) 92, 236
(b) 88, 230
(c) 90, 234
(d) 91, 234

Answer/Explanation

Answer: d
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 18


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

Answer/Explanation

Answer: b
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 19


10. In the nuclear reaction
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 12
What does X stand for?
(a) Electron
(b) Proton
(c) Neutron
(d) Neutrino

Answer/Explanation

Answer: d
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
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei

Answer

Answer: d


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

Answer

Answer: b


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

Answer

Answer: b


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

Answer

Answer: a


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

Answer

Answer: c


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

Answer

Answer: c


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

Answer

Answer: d


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

Answer

Answer: a


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

Answer

Answer: c


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

Answer

Answer: b


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

Answer

Answer: a


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

Answer

Answer: c


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

Answer

Answer: b


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

Answer

Answer: d


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

Answer

Answer: a


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.

Answer

Answer:c


27. Jhe gravitational force between a H-atom and another particle of mass m will be given by Newton’s law: [NCERT Exemplar]
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 2
= magnitude of the potential energy of electron in the H-atom).

Answer

Answer: b


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.
(b) change for α and β radioactivity but not for γ-radioactivity.
(c) change for α-radioactivity but not for others.
(d) change for β-radioactivity but not for others.

Answer

Answer: b


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]
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 3

Answer

Answer: a


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.

Answer

Answer: a


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.

Answer

Answer: b


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.

Answer

Answer: d


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?
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 4
(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.

Answer

Answer: d


34. Radioactivity is the phenomenon associated with
(a) decay of nucleus.
(b) production of radio waves.
(c) transmission of radio waves.
(d) reception of radio waves.

Answer

Answer: a


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

Answer

Answer: b


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.

Answer

Answer: c


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.

Answer

Answer: b


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.

Answer

Answer: c


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

Answer

Answer: d


40. During a mean life of a radioactive element the fraction that disintegrates is
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 6

Answer

Answer: c


41. γ-rays are originated from
(a) nucleus.
(b) outermost shell of nucleus.
(c) innermost shell of nucleus.
(d) outermost shell of atom.

Answer

Answer: a


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

Answer

Answer: c


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

Answer

Answer: b


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

Answer

Answer: b


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

Answer

Answer: d


46. The decay constant of a radioactive substance is X. Its half-life and mean life, respectively are
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 10

Answer

Answer: b


47. Neutrino is a particle, which is chargeless and has spin.

Answer/Explanation

Answer:
Explaination: ±\(\frac{1}{2}\)


48. Isotones have the same number of _________ .

Answer/Explanation

Answer:
Explaination: neutrons


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

Answer/Explanation

Answer:
Explaination: mass defect


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

Answer/Explanation

Answer:
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?

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 20


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

Answer/Explanation

Answer:
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?

Answer/Explanation

Answer:
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]

Answer/Explanation

Answer:
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]

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 21


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

Answer/Explanation

Answer:
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
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 13
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?

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 22
(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?

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 23
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]

Answer/Explanation

Answer:
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.
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 24
In β+ decay, the conversion of proton into neutron and position (β+) takes place.
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 25


60. Which nucleus has greater mean life, A or B?

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 26
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.
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 27


61. Why is a free neutron unstable but a free proton is a stable particle?

Answer/Explanation

Answer:
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.
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 28


62. A neutron strikes a nucleus of \(_{5}^{\mathbf{10}} \mathbf{B}\) and emits an alpha particle. Write down the nuclear reaction for it.

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 29


63. Write the necessary condition required for fusion reaction.

Answer/Explanation

Answer:
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?

Answer/Explanation

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


65. What is the effect of temperature on radioactivity?

Answer/Explanation

Answer:
Explaination:
No effect. Radioactivity is independent of temperature.


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

Answer/Explanation

Answer:
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?

Answer/Explanation

Answer:
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]

Answer/Explanation

Answer:
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.

Answer/Explanation

Answer:
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.

Answer/Explanation

Answer:
Explaination:
Physics MCQs for Class 12 with Answers Chapter 13 Nuclei 30


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.
(c) electromagnetic radiations.
(d) electrons orbiting around the nucleus.

Answer

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.

Answer

Answer: (b) 9 × 1013J


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

Answer

Answer: (b) 7.8 × 10-3


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

Answer

Answer: (b) saturated 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

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

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).

Answer

Answer: (a) and (d).


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.

Answer

Answer: (b) 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

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

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

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

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%

Answer

Answer: (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

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.

Answer

Answer: (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.

Answer

Answer: (b) Plutonium – 239


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

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

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

Answer

Answer: (c) 1015


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

Answer

Answer: (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

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

Answer

Answer: (a) even-even


Fill in the Blanks

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

Answer

Answer: Atomic number, mass number.


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

Answer

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


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

Answer

Answer: Nuclear fusion.


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

Answer

Answer: 2.5.


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

Answer

Answer: Moderator.


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.

Answer

Answer: neutrons, fast, slow.


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

Answer

Answer: 1017 kg m-3.


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

Answer

Answer: 8.5 MeV.


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

Answer

Answer: Helium nucleus, high kinetic energy.


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

Answer

Answer: 200.


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

Answer

Answer: Rutherford, Chadwick.


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

Answer

Answer: 3 : 5.


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

Answer

Answer: Plutonium.


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 ………………..

Answer

Answer: Isotopes.


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

Answer

Answer: Fusion process.


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

Answer

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

Answer: \(_{92}^{235}\)U


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

Answer

Answer: The minimum mass needed for chain reaction.


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

Answer

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
the radioactive radiations are emitted in.the sequence of ………………..

Answer

Answer: ß, α, γ.


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

Answer

Answer: electron.


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

Answer

Answer: Chargeless property and has spin.


Question 23.
Out of α, ß and γ radiations, ……………….. and ……………….. are affected by a magnetic field.

Answer

Answer: Alpha (α) and, beta (ß) radiations.


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