Structure of Atom — 50 MCQs

1. Who proposed the plum pudding model of the atom?

• a) Dalton
• b) J.J. Thomson ✅
• c) Rutherford
• d) Bohr

2. Which particle has a negative charge?

• a) Proton
• b) Electron ✅
• c) Neutron
• d) Positron

3. The number of protons in an atom is called:

• a) Atomic number ✅
• b) Mass number
• c) Atomic mass
• d) Valency

4. Isotopes are atoms of same element which have:

• a) Same mass number
• b) Same atomic number but different mass number ✅
• c) Same number of neutrons
• d) Different chemical properties

5. Rutherford's gold foil experiment led to the discovery of:

• a) Electrons
• b) Thomson model
• c) Nucleus ✅
• d) Orbitals

6. The mass number of an atom equals:

• a) Number of protons only
• b) Number of electrons only
• c) Protons + Neutrons ✅
• d) Protons − Electrons

7. Which quantum number determines the shape of an orbital?

• a) Azimuthal quantum number (l) ✅
• b) Principal quantum number (n)
• c) Magnetic quantum number (m)
• d) Spin quantum number (s)

8. Pauli exclusion principle states that:

• a) Electrons occupy lowest energy orbitals first
• b) No two electrons in an atom can have same set of four quantum numbers ✅
• c) Electrons fill degenerate orbitals singly
• d) Electrons behave as waves

9. Hund's rule is about:

• a) Energy of orbitals
• b) Maximum multiplicity (single occupancy of degenerate orbitals first) ✅
• c) Exclusion of electrons
• d) Electron spin pairing is preferred

10. Which is the correct electronic configuration for O (atomic number 8)?

• a) 1s2 2s2 2p3
• b) 1s2 2s2 2p4 ✅
• c) 1s2 2s2 2p6
• d) 1s2 2s1 2p5

11. The principal quantum number (n) indicates:

• a) Size and energy level of orbital ✅
• b) Shape of orbital
• c) Orientation in space
• d) Spin of electron

12. Atomic number of an atom is equal to the number of:

• a) Protons ✅
• b) Neutrons
• c) Electrons only
• d) Protons + Neutrons

13. Which of the following has zero net charge?

• a) Cation
• b) Anion
• c) Neutral atom ✅
• d) Radical

14. The spin quantum number can have values:

• a) 0, ±1
• b) +1/2 or −1/2 ✅
• c) 0 or 1
• d) Any integer

15. Which spectrum arises from electronic transitions within an atom?

• a) Atomic emission/absorption spectrum ✅
• b) Molecular rotational spectrum
• c) Nuclear magnetic resonance
• d) Infrared vibrational spectrum

16. Which of the following best describes a photon?

• a) A tiny particle of matter
• b) A quantum of electromagnetic radiation ✅
• c) A charged particle
• d) A neutron

17. The discovery of the neutron is credited to:

• a) Rutherford
• b) James Chadwick ✅
• c) Thomson
• d) Bohr

18. The Bohr model was primarily successful in explaining the spectrum of:

• a) Hydrogen atom ✅
• b) Helium atom
• c) Sodium atom
• d) Oxygen atom

19. The relation λ = h/p expresses the wave nature of particles. This is known as:

• a) Heisenberg uncertainty principle
• b) De Broglie equation ✅
• c) Planck's equation
• d) Schrödinger equation

20. Heisenberg uncertainty principle relates uncertainties in:

• a) Energy and time only
• b) Position and momentum ✅
• c) Charge and mass
• d) Wavelength and frequency

21. Which orbital corresponds to l = 2?

• a) s orbital
• b) p orbital
• c) d orbital ✅
• d) f orbital

22. The magnetic quantum number (m) indicates:

• a) Energy level
• b) Orientation of orbital in space ✅
• c) Shape of orbital
• d) Spin direction

23. A cation is formed when an atom:

• a) Gains electron
• b) Loses electron ✅
• c) Gains proton
• d) Loses proton

24. The most probable distance of electron from nucleus in hydrogen atom is given by:

• a) Bohr radius ✅
• b) de Broglie wavelength
• c) Compton wavelength
• d) Planck length

25. The exchange of which particle changes one element into another?

• a) Electron
• b) Proton (change in proton number changes element) ✅
• c) Neutron
• d) Photon

26. Which scientist explained the photoelectric effect using photons?

• a) Bohr
• b) Einstein ✅
• c) Planck
• d) de Broglie

27. The Aufbau principle helps to determine:

• a) Order of filling of orbitals ✅
• b) Spin orientation
• c) Nuclear stability
• d) Types of chemical bonds

28. Which of the following is NOT a quantum number?

• a) Principal
• b) Azimuthal
• c) Magnetic
• d) Electrical ✅

29. The K-shell corresponds to n =

• a) 1 ✅
• b) 2
• c) 3
• d) 4

30. The orbital with l = 0 is called:

• a) s orbital ✅
• b) p orbital
• c) d orbital
• d) f orbital

31. Which of the following particles has nearly same mass as proton?

• a) Electron
• b) Neutron ✅
• c) Positron
• d) Alpha particle

32. The term 'orbitals' was introduced by:

• a) Bohr
• b) Schrödinger ✅
• c) Rutherford
• d) Heisenberg

33. Which is true for isotones?

• a) Same atomic number
• b) Same mass number
• c) Same number of neutrons ✅
• d) Same chemical properties

34. The de Broglie wavelength of a particle is inversely proportional to its:

• a) Momentum ✅
• b) Energy
• c) Mass only
• d) Charge

35. The number of orbitals in a shell with principal quantum number n is:

• a) n^2 ✅
• b) 2n^2
• c) 2n
• d) n

36. The total number of electrons that can be accommodated in the second shell (n=2) is:

• a) 8 ✅
• b) 2
• c) 18
• d) 4

37. Which particle determines the identity of an element?

• a) Proton ✅
• b) Neutron
• c) Electron
• d) Positron

38. The concept of quantized energy levels was first suggested by:

• a) Rutherford
• b) Planck ✅
• c) Dalton
• d) Bohr

39. In an atom, electrons in orbitals with higher n have:

• a) Lower energy
• b) Higher energy ✅
• c) Same energy
• d) No energy
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40. Which of the following is true for isobars?

• a) Same atomic number
• b) Same mass number ✅
• c) Same number of neutrons
• d) Same chemical properties

41. The energy of a photon is given by:

• a) E = hν ✅
• b) E = mc^2
• c) E = 1/2 mv^2
• d) E = λ/p

42. The maxima in photoelectric effect is dependent on:

• a) Intensity of light
• b) Frequency of light (threshold concept) ✅
• c) Color of emitter
• d) Temperature only

43. The total number of orbitals in n = 3 shell is:

• a) 9 ✅
• b) 3
• c) 6
• d) 18

44. The shape of p-orbital is:

• a) Spherical
• b) Dumbbell-shaped ✅
• c) Cloverleaf
• d) Complex

45. Which orbital can hold a maximum of 10 electrons?

• a) s
• b) p
• c) d ✅
• d) f

46. The term 'valence electrons' refers to electrons in:

• a) Inner shell
• b) Outermost shell ✅
• c) Nucleus
• d) Any filled shell

47. The mass of electron is approximately:

• a) 1.67×10^-27 kg
• b) 9.11×10^-31 kg ✅
• c) 1.67×10^-26 kg
• d) 1.67×10^-30 kg

48. The nucleus contains:

• a) Electrons
• b) Protons and neutrons ✅
• c) Protons only
• d) Neutrons only

49. An atom of mass number 23 and atomic number 11 is:

• a) 11 protons, 12 electrons
• b) 11 protons, 12 neutrons ✅
• c) 23 protons
• d) 12 protons, 11 neutrons

50. The maximum number of electrons in a shell is given by:

• a) n
• b) 2n^2 ✅
• c) n^2
• d) 4n