Summary & 50 MCQs with Answers
This chapter covers the structure of atoms, Bohr model, energy levels, spectra, quantum numbers, and basic atomic properties. It explains the behavior of electrons in shells, transitions between energy levels, and emission/absorption spectra.
1. The Bohr model of hydrogen atom explains:
A) Atomic spectra ✅
B) Nuclear fission
C) Chemical bonding
D) Radioactivity
2. Electrons in an atom occupy:
A) Discrete energy levels ✅
B) Continuous energy levels
C) Only ground state
D) Random positions
3. The Rydberg constant is related to:
A) Hydrogen spectral lines ✅
B) Nuclear decay
C) Electron spin
D) Magnetic moment
4. Ground state of hydrogen atom corresponds to:
A) n = 1 ✅
B) n = 2
C) n = 0
D) n = ∞
5. First excited state of hydrogen atom corresponds to:
A) n = 2 ✅
B) n = 1
C) n = 3
D) n = 0
6. Energy of electron in nth orbit of hydrogen atom is:
A) E_n = -13.6/n² eV ✅
B) E_n = 13.6 n² eV
C) E_n = -13.6 n eV
D) E_n = 0
7. Radius of nth orbit in Bohr model is proportional to:
A) n² ✅
B) n
C) 1/n²
D) 1/n
8. Spectral lines in hydrogen atom are due to:
A) Electron transitions between orbits ✅
B) Proton movement
C) Neutron decay
D) Nuclear fission
9. Lyman series corresponds to transitions ending at:
A) n = 1 ✅
B) n = 2
C) n = 3
D) n = ∞
10. Balmer series corresponds to transitions ending at:
A) n = 2 ✅
B) n = 1
C) n = 3
D) n = ∞
11. Paschen series corresponds to transitions ending at:
A) n = 3 ✅
B) n = 1
C) n = 2
D) n = 4
12. Ionization energy of hydrogen atom in ground state is:
A) 13.6 eV ✅
B) 10.2 eV
C) 3.4 eV
D) 1.36 eV
13. Bohr’s quantization condition is:
A) mvr = n h/2π ✅
B) mvr = h
C) mvr² = nh
D) mvr = n² h
14. Maximum number of electrons in n-th shell is:
A) 2n² ✅
B) n²
C) 2n
D) n
15. Quantum number ‘l’ defines:
A) Angular momentum ✅
B) Principal energy
C) Spin
D) Magnetic orientation
16. Magnetic quantum number ‘m’ defines:
A) Orientation of orbital ✅
B) Spin of electron
C) Energy level
D) Type of atom
17. Spin quantum number of electron can be:
A) +1/2 or -1/2 ✅
B) 0 or 1
C) 1/2 or 3/2
D) Only +1/2
18. Pauli exclusion principle states:
A) No two electrons can have same set of four quantum numbers ✅
B) Electrons occupy lowest energy first
C) Orbitals are spherical
D) Energy levels are quantized
19. Hund’s rule of maximum multiplicity states:
A) Electrons occupy degenerate orbitals singly first ✅
B) Electrons pair first
C) Only two electrons per atom
D) Electrons skip orbitals
20. Energy difference between two levels is emitted as:
A) Photon ✅
B) Electron
C) Proton
D) Neutron
21. Frequency of emitted photon is related to:
A) ΔE/h ✅
B) ΔE × h
C) ΔE²/h
D) h/ΔE
22. Atomic spectra are:
A) Discrete lines ✅
B) Continuous bands
C) Random
D) Not observable
23. Bohr model fails for:
A) Multi-electron atoms ✅
B) Hydrogen atom
C) Ionized hydrogen
D) Isolated electron
24. The angular momentum of electron in Bohr’s model:
A) Quantized ✅
B) Continuous
C) Zero
D) Random
25. The emission spectrum is due to:
A) Electron falling to lower orbit ✅
B) Electron ionization
C) Proton movement
D) Nuclear decay
26. Absorption spectrum is observed when:
A) Electron absorbs energy to higher orbit ✅
B) Electron falls down
C) Proton absorbs energy
D) Neutron decays
27. Principal quantum number n can take values:
A) 1,2,3,... ✅
B) 0,1,2
C) 1,3,5
D) Negative integers
28. Electron in higher orbit has:
A) Higher energy ✅
B) Lower energy
C) Same energy
D) Zero energy
29. Atomic number (Z) represents:
A) Number of protons ✅
B) Number of neutrons
C) Mass number
D) Number of electrons only
30. Mass number (A) is:
A) Protons + neutrons ✅
B) Protons only
C) Neutrons only
D) Electrons only
31. Isotopes differ in:
A) Number of neutrons ✅
B) Number of protons
C) Chemical properties
D) Electron number
32. Isobars differ in:
A) Number of protons ✅
B) Number of neutrons
C) Mass number
D) Energy
33. Ionization energy increases:
A) Across a period ✅
B) Down a group
C) Randomly
D) Never
34. Ionization energy decreases:
A) Down a group ✅
B) Across a period
C) Randomly
D) Never
35. Electron affinity is:
A) Energy released on gaining electron ✅
B) Energy required to remove electron
C) Mass change
D) Proton number
36. The ground state of helium has electrons in:
A) 1s² ✅
B) 2s¹
C) 2p²
D) 1p²
37. Excited state of helium may be:
A) 1s¹2s¹ ✅
B) 1s²
C> 2s²
D> 1p²
38. Spectroscopic notation of hydrogen 3rd orbit:
A) 3 → n=3 ✅
B) n=1
C) n=2
D) n=4
39. The ground state of lithium atom is:
A) 1s² 2s¹ ✅
B) 1s² 2p¹
C) 1s² 2s²
D) 1s¹ 2s²
40. Aufbau principle states:
A) Electrons fill lowest energy first ✅
B) Electrons fill highest first
C) Electrons pair randomly
D) Electrons occupy one orbital only
41. Effective nuclear charge is:
A) Net positive charge experienced by electron ✅
B) Total proton charge
C) Total neutron charge
D) Zero
42. Atomic radius decreases:
A) Across a period ✅
B) Down a group
C) Randomly
D) Never
43. Atomic radius increases:
A) Down a group ✅
B) Across a period
C) Randomly
D) Never
44. First ionization energy of sodium:
A) 496 kJ/mol ✅
B) 520 kJ/mol
C) 1312 kJ/mol
D) 237 kJ/mol
45. Hydrogen atom spectrum studied by:
A) Bohr model ✅
B) Rutherford only
C) Thomson
D) Dalton
46. Bohr radius is:
A) 0.529 × 10⁻¹⁰ m ✅
B) 1.0 × 10⁻¹⁰ m
C) 0.1 × 10⁻¹⁰ m
D) 5.29 × 10⁻¹² m
47. Rydberg formula gives:
A) Wavelength of spectral lines ✅
B) Radius of atom
C) Energy of nucleus
D) Ionization energy
48. De Broglie wavelength is associated with:
A) Electron ✅
B) Proton
C) Neutron
D) Photon
49. Dual nature of electron is:
A) Particle + Wave ✅
B) Only particle
C) Only wave
D) Neither
50. Heisenberg uncertainty principle relates:
A) Δx × Δp ≥ h/4π ✅
B) E × t = 0
C) m × v = 0
D) λ × f = c