Nuclei - Class 12 Physics MCQs

Chapter Summary

The Nuclei chapter covers nuclear structure, properties of nucleons, nuclear binding energy, radioactivity, decay laws, nuclear fission and fusion, mass-energy relation, and applications of isotopes. It explains the stability of nuclei, mass defect, binding energy per nucleon, liquid drop model, and semi-empirical mass formula.

1. The charge of a proton is:

A) +1.6 × 10⁻¹⁹ C ✅

B) -1.6 × 10⁻¹⁹ C

C) 0

D) +3.2 × 10⁻¹⁹ C

2. The nucleus of an atom consists of:

A) Electrons and protons

B) Protons and neutrons ✅

C) Protons only

D) Neutrons only

3. The radius of nucleus (R) is proportional to:

A) 1/A

B) A

C) A^(1/3) ✅

D) √A

4. Mass defect is:

A) Difference between mass of nucleus and sum of masses of nucleons ✅

B) Mass of proton minus mass of neutron

C) Mass of atom minus mass of electrons

D) Binding energy per nucleon

5. Nuclear binding energy is highest for:

A) Hydrogen

B) Uranium

C) Iron-56 ✅

D) Helium

6. Radioactive decay is:

A) Spontaneous transformation of nucleus ✅

B) Chemical reaction

C) Ionization process

D) Electron transition

7. Half-life of a radioactive substance is:

A) Time for total decay

B) Time for half of nuclei to decay ✅

C) Time for 1/4th nuclei to decay

D) Time for one nucleus to decay

8. The liquid drop model explains:

A) Nuclear fission and binding energy trends ✅

B) Atomic spectra

C) Electron shells

D) Chemical bonding

9. Nuclear fission is:

A) Splitting of heavy nucleus into lighter nuclei ✅

B) Combining of nuclei

C) Alpha decay

D) Beta decay

10. Nuclear fusion releases energy because:

A) Mass increases

B) Mass defect converts to energy ✅

C) Electrons are emitted

D) Neutrons are absorbed

11. Alpha particle consists of:

A) 2 protons + 2 neutrons ✅

B) 1 proton + 1 neutron

C) 1 electron + 1 proton

D) 2 electrons

12. Beta decay involves emission of:

A) Electron or positron ✅

B) Alpha particle

C) Photon

D) Neutron

13. Gamma rays are:

A) High energy photons ✅

B) Electrons

C) Neutrons

D) Alpha particles

14. Activity of radioactive substance decreases over time because:

A) Number of undecayed nuclei decreases ✅

B) Mass decreases

C) Protons decay

D) Electrons escape

15. Law of radioactive decay is:

A) dN/dt = -λN ✅

B) N = constant

C) dN/dt = +λN

D) None of the above

16. Mean life of radioactive nuclei is:

A) Average life before decay ✅

B) Half-life

C) Time for 1/4 decay

D) Infinite

17. Unit of activity of a radioactive substance is:

A) Becquerel (Bq) ✅

B) Coulomb

C) Watt

D) Joule

18. Neutron was discovered by:

A) James Chadwick ✅

B) Rutherford

C) J.J. Thomson

D) Bohr

19. Mass-energy equivalence is given by:

A) E = mc² ✅

B) F = ma

C) E = hv

D) p = mv

20. Binding energy per nucleon is maximum for:

A) Iron-56 ✅

B) Uranium

C) Hydrogen

D) Helium

21. Nuclear fission produces:

A) Energy + 2–3 neutrons ✅

B) Only energy

C) Only neutrons

D) Electrons

22. Critical mass in fission refers to:

A) Minimum mass for chain reaction ✅

B) Maximum mass

C) Half of mass

D) Mass of proton

23. Nuclear fusion occurs in:

A) Stars ✅

B) Nuclear reactors

C) Bombs

D) Electron tubes

24. Neutrino was proposed to conserve:

A) Energy, momentum and spin ✅

B) Mass only

C) Charge only

D) Electron number only

25. Isotopes have same:

A) Atomic number ✅

B) Mass number

C) Number of neutrons

D) Binding energy

26. Isobars have same:

A) Mass number ✅

B) Atomic number

C) Neutrons

D) Electron configuration

27. Isotones have same:

A) Number of neutrons ✅

B) Protons

C) Mass number

D) Charge

28. Geiger-Müller counter detects:

A) Radioactive particles ✅

B) Light

C) Magnetic field

D) Sound waves

29. Alpha particle has:

A) +2 charge ✅

B) +1 charge

C) 0 charge

D) -1 charge

30. Beta-minus decay converts:

A) Neutron → proton + electron + antineutrino ✅

B) Proton → neutron

C) Neutron → electron

D) Electron → proton

31. Beta-plus decay converts:

A) Proton → neutron + positron + neutrino ✅

B) Neutron → proton

C) Electron → proton

D) Proton → electron

32. Electron capture involves:

A) Proton + electron → neutron + neutrino ✅

B) Neutron → proton + electron

C) Electron emission

D) Alpha emission

33. Nuclear reaction in which nucleus splits into two fragments:

A) Fission ✅

B) Fusion

C) Alpha decay

D) Beta decay

34. Energy released per fission of U-235 nucleus is approximately:

A) 200 MeV ✅

B) 10 MeV

C) 1 MeV

D) 1000 MeV

35. Fusion reactions power:

A) Stars like Sun ✅

B) Coal plants

C) Fission reactors

D) Batteries

36. Alpha particle is same as:

A) Helium nucleus ✅

B) Hydrogen nucleus

C) Proton

D) Electron

37. Neutron to proton ratio increases with:

A) Increase in atomic number ✅

B) Decrease in mass number

C) Constant number of protons

D) Radioactive decay

38. Nucleus with equal number of protons and neutrons is:

A) Stable (for light nuclei) ✅

B) Always unstable

C) Radioactive

D) Always undergoes fission

39. Radioactive isotopes used in medical diagnosis are called:

A) Tracers ✅

B) Fuel

C) Reactants

D) Catalysts

40. Geiger-Müller counter is used to detect:

A) Radioactive particles ✅

B) Light waves

C) Sound waves

D) Magnetic fields

41. Nuclear force is:

A) Short-range attractive force between nucleons ✅

B) Gravitational force

C) Electromagnetic force

D) Long-range force

42. Semi-empirical mass formula is based on:

A) Liquid drop model ✅

B) Quantum model

C) Electron shell model

D) Chemical bonding model

43. Average binding energy per nucleon for iron-56 is about:

A) 8.8 MeV ✅

B) 1 MeV

C) 0.5 MeV

D) 10 MeV

44. Liquid drop model explains:

A) Nuclear fission and binding energy trends ✅

B) Atomic spectra

C) Electron shells

D) Chemical bonding

45. Excess neutrons in heavy nuclei cause:

A) Beta-minus decay ✅

B) Alpha decay

C) Gamma emission

D) Fission

46. Mass defect arises due to:

A) Conversion of mass to binding energy ✅

B) Proton emission

C) Electron capture

D) Neutron decay

47. Strongest nuclear force acts between:

A) Nucleons ✅

B) Electrons

C) Protons and electrons

D) Neutrons only

48. Nuclear reactor fuel is commonly:

A) Uranium-235 or Plutonium-239 ✅

B) Hydrogen

C) Helium

D) Iron

49. Moderator in nuclear reactor is used to:

A) Slow down neutrons ✅

B) Increase neutron speed

C) Absorb electrons

D) Cool fuel

50. Control rods in reactor are used to:

A) Absorb excess neutrons ✅

B) Emit neutrons

C) Produce energy

D) Heat moderator