# Class 12 Physics Chapter 13 Nuclei with MCQs with Answers

## CBSE : NCERT Solutions for Class 12 Physics Chapter 13 Nuclei MCQ’s with Answers

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### NCERT Physics MCQs for Class 12 Physics Chapter 13 Nuclei PDF

Q1. Which of the following nuclei is most stable
(a) even-even
(b) odd-odd
(c) odd-even
(d) even-odd

Q2. 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.

Q3. Consider the fission reaction :
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

Q4. 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.

Q5. Which of the following is the best nuclear fuel.
(a) Thorium-236
(b) Plutonium – 239
(c) Neptunium-239
(d) Uranium-236.

Q6. 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.

Q7. 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 C²
(b) Q = (Mp – Md – Mc) C²
(c) Q = (Mp – Md)C²
(d) Q = (Mp – md – 2Me)C².

Answer:(c) Q = (Mp – Md)C²

Q8. 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%

Q9. For thorium A = 232 and Z = 90. At the end of some radioactive disintegrations we obtain an isotope of lead with 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

Q10. 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.

Q11. 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.

Q12. 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.

Q13. 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.

Q14. 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 – Eb
(d) Ea + 3Eb + E = 0

Answer:(a) Ea + E = 3 Eb

Q15. 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

Q16. 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.

Q17. 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.

Q18. Chadwick was awarded the Nobel prize in Physics in 1935 for his discovery of:
(a) electron
(b) proton
(c) neutron
(d) None of these

Q19. Alpha particle emitted from a radioactive material are:
(a) Helium nuclei
(b) Hydrogen nuclei
(c) Lithium nuclei
(d) None of the above

Q20. The half life of a radioactive decay is n times its mean life, n is equal to:
(a) 0.6930
(b) 0.0693
(c) 0.9865
(d) 0.3070

Q21. Rutherford is the unit of:
(b) energy
(c) photoelectric current
(d) magnetic field

Q22. According to Yukawa’s theory of nuclear forces, the origin of nuclear force between nucleons is due to the exchange of
(a) mesons
(b) photons
(c) electrons
(d) positrons

Q23. Radius of 1st Bohr orbit is a0 (= 0.529 Å) What is the radius of 2nd Bohr orbit?
(a) 10-8
(b) 2a0
(c) 4a0
(d) 2√2a0

Q24. The Bohr model of atom:
(a) assumes that the angular momentum of electron is quantized
(b) uses Einstein’s photoelectric equation
(c) predicts continuous emission spectra for atoms
(d) predicts the same emission spectra for all types of atoms

Answer:(a) assumes that the angular momentum of electron is quantized

Q25. If radio active nuclei emits β-particle, then mass-number:
(a) increased by 1 unit
(b) decreases by 1 unit
(c) increases by 2 unit
(d) decreases by 2 unit