30 *most important MCQs* with answers on the topic of "Atoms and Nuclei" for Class 12 Physics students
Atoms and Atomic Models
1. Rutherford’s alpha particle experiment proved the existence of the
- (a) Electron
- (b) Proton
- (c) Neutron
- (d) Nucleus
- *Answer:* (d) Nucleus
2. The radius of the nth orbit of the hydrogen atom (Bohr’s model) is proportional to:
- (a) n^2
- (b) n
- (c) 1/n
- (d) n^3
- *Answer:* (a) n^2
3. The Balmer series lies in which spectrum?
- (a) Ultraviolet
- (b) Visible
- (c) Infrared
- (d) Partially Visible
- *Answer:* (b) Visible
4. Why was Rutherford’s atomic model unstable?
- (a) Electrons radiate energy while revolving and fall into the nucleus
- (b) Nucleus repels electrons
- (c) Electrons do not remain in orbit
- (d) Atoms are neutral
- *Answer:* (a) Electrons radiate energy while revolving and fall into the nucleus
5. Who explained the splitting of spectral lines in a magnetic field?
- (a) Zeeman
- (b) Bohr
- (c) Sommerfeld
- (d) Einstein
- *Answer:* (a) Zeeman
### Nuclear Structure and Properties
6. The mass of a neutron is:
- (a) 1.00866 u
- (b) 1.0866 u
- (c) 1.866 u
- (d) 0.1866 u
- *Answer:* (a) 1.00866 u
7. Isobars have the same:
- (a) Mass number (A)
- (b) Atomic number (Z)
- (c) Number of neutrons (N)
- (d) All of these
- *Answer:* (a) Mass number (A)
8. Which quantity is not conserved in a nuclear reaction?
- (a) Mass
- (b) Charge
- (c) Momentum
- (d) Energy
- *Answer:* (a) Mass
9. Parent and daughter nuclei in beta decay are:
- (a) Isotopes
- (b) Isobars
- (c) Isotones
- (d) Isomers
- *Answer:* (b) Isobars
10. The energy equivalent to one atomic mass unit is:
- (a) 1.6 × 10^-19 J
- (b) 6.02 × 10^23 J
- (c) 9.31 MeV
- (d) 931 MeV
- *Answer:* (d) 931 MeV
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Chapter wise Extra Q & A Sets (Physics, Class 12) |
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Electric Charges and Fields |
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Electrostatic Potential and Capacitance |
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Current Electricity |
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Moving Charges and Magnetism |
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Magnetism and Matter |
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Electromagnetic Induction |
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Alternating Current (AC) |
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Electromagnetic Waves |
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Ray Optics and Optical Instruments |
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Wave Optics |
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Dual Nature of Radiation and Matter |
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Atoms |
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Nuclei |
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Semiconductor Electronics: Materials, Devices and Simple Circuits |
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Communication System |
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Radioactivity
11. Beta rays emitted by radioactive materials are:
- (a) Electromagnetic radiation
- (b) The electrons orbiting the nucleus
- (c) Charged particles from the nucleus
- (d) Neutral particles
- *Answer:* (c) Charged particles from the nucleus [1]
12. Gamma rays are deflected:
- (a) By electric field only
- (b) By magnetic field only
- (c) By both electric and magnetic fields
- (d) By neither electric nor magnetic fields
- *Answer:* (d) By neither electric nor magnetic fields
13. The process of radioactivity is:
- (a) Irreversible
- (b) Self-disintegration
- (c) Spontaneous
- (d) All of the above
- *Answer:* (d) All of the above
14. Radioactive decay law is governed by:
- (a) Linear law
- (b) Exponential law
- (c) Logarithmic law
- (d) Parabolic law
- *Answer:* (b) Exponential law
15. In alpha decay, which particle is emitted?
- (a) Helium nucleus
- (b) Electron
- (c) Neutron
- (d) Photon
- *Answer:* (a) Helium nucleus
Nuclear Forces & Stability
16. Nuclear forces are:
- (a) Spin dependent and non-central
- (b) Spin dependent but central
- (c) Spin independent and non-central
- (d) Spin independent and central
- *Answer:* (a) Spin dependent and non-central
17. Which is a non-central force?
- (a) Electrostatic force
- (b) Nuclear force
- (c) Gravitational force
- (d) Spring force
- *Answer:* (b) Nuclear force
18. Nuclear density is:
- (a) Same for all nuclei
- (b) More for heavy nuclei
- (c) Less for light nuclei
- (d) Variable
- *Answer:* (a) Same for all nuclei
19. What maintains the stability of a nucleus?
- (a) Repulsion between nucleons
- (b) Binding energy
- (c) Loss of mass
- (d) Kinetic energy
- *Answer:* (b) Binding energy
20. The radius of the nucleus (R) is proportional to:
- (a) A (mass number)
- (b) √A
- (c) A^(1/3)
- (d) 1/A
- *Answer:* (c) A^(1/3)
Nuclear Reactions
21. Which quantity remains constant in a nuclear reaction?
- (a) Number of atoms
- (b) Number of nucleons
- (c) Energy
- (d) Mass alone
- *Answer:* (b) Number of nucleons
22. Particles that can be added to a nucleus without changing its chemical properties:
- (a) Neutrons
- (b) Electrons
- (c) Protons
- (d) Alpha particles
- *Answer:* (a) Neutrons
23. For a nuclear fusion process, suitable nuclei are:
- (a) Any nuclei
- (b) Heavy nuclei
- (c) Lighter nuclei
- (d) Nuclei in the middle of the periodic table
- *Answer:* (c) Lighter nuclei [1][3]
24. The light energy emitted by a star is due to:
- (a) Fusion of nuclei
- (b) Burning of nuclei
- (c) Fission of nuclei
- (d) Solar reflection
- *Answer:* (a) Fusion of nuclei
25. In fission, the sum of masses of products is:
- (a) Equal to reactants
- (b) Less than reactants
- (c) Greater than reactants
- (d) Unchanged
- *Answer:* (b) Less than reactants
Atomic and Nuclear Definitions
26. The main feature of Bohr’s atomic model is:
- (a) Quantization of electron orbits
- (b) Existence of nucleus
- (c) Neutron presence
- (d) Proton orbiting nucleus
- *Answer:* (a) Quantization of electron orbits
27. Chemical properties of isotopes are:
- (a) Identical
- (b) Different
- (c) Partially similar
- (d) None
- *Answer:* (a) Identical
28. Isotopes differ in:
- (a) Atomic number
- (b) Chemical properties
- (c) Mass number
- (d) None
- *Answer:* (c) Mass number
29. The charge of a beta particle is:
- (a) –1.6 × 10^-19 C
- (b) +1.6 × 10^-19 C
- (c) Zero
- (d) 9 × 10^9 C
- *Answer:* (a) –1.6 × 10^-19 C
30. An atom stays in its excited state for about:
- (a) 10 microseconds
- (b) 10 milliseconds
- (c) 10 nanoseconds
- (d) 10 seconds
- *Answer:* (c) 10 nanoseconds
