Below is a complete set of 60 multiple-choice questions (MCQs) on *Structure of Atom*, covering easy, moderate, and tough levels. Each question includes four options, and answers are provided at the end.
Easy Level (30%)
1. **Who discovered the electron?**
a) Rutherford
b) J.J. Thomson
c) Bohr
d) Chadwick
2. **What is the charge of a proton?**
a) Negative
b) Positive
c) Neutral
d) Variable
3. **What is the atomic number of hydrogen?**
a) 0
b) 1
c) 2
d) 3
4. **Who is credited with the discovery of the neutron?**
a) Rutherford
b) Bohr
c) Chadwick
d) Thomson
5. **What did Rutherford’s gold foil experiment discover?**
a) Electrons are in fixed orbits
b) Atoms have a dense nucleus
c) Electrons are in the nucleus
d) Atoms are indivisible
6. **Which particle has no charge?**
a) Proton
b) Electron
c) Neutron
d) None of these
7. **What is the atomic number of carbon?**
a) 6
b) 12
c) 14
d) 16
8. **What is the relative charge of an electron?**
a) +1
b) 0
c) -1
d) +2
9. **Who proposed the model of the atom with electrons in defined orbits?**
a) Rutherford
b) Bohr
c) Thomson
d) Dalton
10. **The atomic number represents the number of:**
a) Neutrons only
b) Protons only
c) Electrons only
d) Protons and electrons
11. **What is the mass number of an atom?**
a) Number of protons
b) Number of neutrons
c) Sum of protons and neutrons
d) Sum of electrons and neutrons
12. **Which of the following is an isotope of hydrogen?**
a) Helium-4
b) Hydrogen-2
c) Carbon-12
d) Uranium-238
13. **Which subatomic particle was discovered first?**
a) Neutron
b) Electron
c) Proton
d) Nucleus
14. **What is the mass of a neutron compared to a proton?**
a) Equal
b) Half
c) Double
d) Zero
15. **What is the electronic configuration of helium?**
a) 1
b) 2
c) 1,1
d) 2,2
16. **The atomic number of nitrogen is 7. Its electronic configuration is:**
a) 2,5
b) 2,3
c) 2,6
d) 3,4
17. **Which element has atomic number 8?**
a) Oxygen
b) Nitrogen
c) Carbon
d) Fluorine
18. **What is the symbol for an electron?**
a) p
b) n
c) e
d) A
19. **An atom with 6 protons, 6 electrons, and 6 neutrons has a mass number of:**
a) 6
b) 12
c) 18
d) 24
20. **Which isotope of carbon is radioactive and used in dating?**
a) Carbon-12
b) Carbon-14
c) Carbon-16
d) Carbon-10
---
### **Moderate Level (40%)**
21. **What was the major flaw in Rutherford's atomic model?**
a) No nucleus
b) Did not account for electron stability
c) No charge on protons
d) Included neutrons
22. **Which of the following explains why Bohr’s model is stable?**
a) Presence of nucleus
b) Quantized electron orbits
c) Alpha particles in atoms
d) Electrons at rest
23. **The atomic mass of an element is determined by:**
a) Only protons
b) Only electrons
c) Protons and neutrons
d) Neutrons only
24. **In Rutherford's experiment, what did most alpha particles passing through the gold foil indicate?**
a) Nucleus has a large volume
b) Most of the atom is empty space
c) Electrons are inside the nucleus
d) Atoms are solid
25. **What type of radiation was used in Rutherford’s experiment?**
a) Beta particles
b) Gamma rays
c) Alpha particles
d) Cathode rays
26. **What is the atomic number of chlorine?**
a) 10
b) 17
c) 18
d) 19
27. **How many electrons are in the first shell of an atom?**
a) 2
b) 8
c) 10
d) 12
28. **Which isotope is commonly used in archaeological dating?**
a) Uranium-238
b) Carbon-14
c) Chlorine-35
d) Nitrogen-15
29. **An atom has an atomic number of 8. How many electrons does it have?**
a) 6
b) 8
c) 10
d) 12
30. **What is the electronic configuration of neon?**
a) 2,8
b) 2,8,1
c) 2,8,2
d) 1,8
31. **Which element has an atomic number of 20?**
a) Magnesium
b) Potassium
c) Calcium
d) Iron
32. **What is the charge of a neutron?**
a) Positive
b) Negative
c) Neutral
d) None of these
33. **What do isotopes of an element have in common?**
a) Same atomic mass
b) Same number of neutrons
c) Same atomic number
d) Same mass number
34. **What is the application of Cobalt-60?**
a) Archaeological dating
b) Power generation
c) Cancer radiotherapy
d) Carbon dating
35. **Which element is an isotope of chlorine?**
a) Chlorine-35
b) Carbon-12
c) Oxygen-18
d) Nitrogen-14
36. **How many protons does an element with atomic number 12 have?**
a) 10
b) 11
c) 12
d) 14
37. **Which isotope of hydrogen is used in nuclear fusion?**
a) Protium
b) Deuterium
c) Tritium
d) Hydrogen-1
38. **The atomic number of uranium is 92. How many protons does uranium have?**
a) 92
b) 146
c) 238
d) 144
39. **An isotope of an element has:**
a) Different atomic number
b) Same atomic number but different atomic mass
c) Same atomic mass but different atomic number
d) Same atomic number and mass
40. **What is the mass number of an isotope of uranium with 146 neutrons?**
a) 235
b) 238
c) 234
d) 239
---
### **Tough Level (30%)**
41. **Which isotope of uranium is used in nuclear reactors?**
a) Uranium-235
b) Uranium-238
c) Uranium-234
d) Uranium-236
42. **How many protons are in an atom of carbon-14?**
a) 12
b) 6
c) 14
d) 8
43. **What is the electronic configuration of calcium (atomic number 20)?**
a) 2,8,8
b) 2,8,8,2
c) 2,8,7,3
d) 2,8,9,1
44. **What is the major flaw in Rutherford’s atomic model?**
a) Electrons emit energy continuously
b) Electrons have no charge
c) Nucleus is very large
d) None of the above
45. **Why is the nucleus stable in Bohr’s model?**
a) Electrons emit energy continuously
b) Electrons are in stable orbits
c) Protons are outside the nucleus
d) Nucleus is very small
46. **The discovery of neutron helped to explain:**
a) Mass
of the atom
b) Atomic number
c) Charge of atom
d) Volume of the atom
47. **Which of the following elements has the smallest atomic radius?**
a) Sodium
b) Magnesium
c) Carbon
d) Neon
48. **The mass number of an element with 17 protons and 18 neutrons is:**
a) 35
b) 36
c) 17
d) 18
49. **Which isotope of hydrogen is radioactive?**
a) Deuterium
b) Protium
c) Tritium
d) None
50. **What is the symbol for tritium?**
a) H-1
b) H-2
c) H-3
d) H-4
51. **Which particle has the highest energy in an atom?**
a) Proton
b) Neutron
c) Inner-shell electron
d) Outer-shell electron
52. **The isotope carbon-14 is used for dating because it is:**
a) Stable
b) Radioactive
c) Reactive
d) Neutral
53. **An atom with atomic number 19 has how many electrons?**
a) 17
b) 18
c) 19
d) 20
54. **Which element has a full outer electron shell in the second period?**
a) Helium
b) Neon
c) Argon
d) Krypton
55. **The electrons in which shell have the highest energy?**
a) K
b) L
c) M
d) N
56. **The isotope with atomic number 1 and atomic mass 2 is:**
a) Protium
b) Tritium
c) Deuterium
d) Hydrogen
57. **What is the most stable electron configuration?**
a) 2,8
b) 2,8,8
c) 2,8,18
d) 2,8,18,32
58. **Which atomic model describes electrons in clouds?**
a) Rutherford
b) Thomson
c) Quantum mechanical
d) Bohr
59. **Which isotope has 12 protons and 13 neutrons?**
a) Magnesium-25
b) Magnesium-24
c) Magnesium-23
d) Magnesium-22
60. **Which of the following particles has the least mass?**
a) Neutron
b) Proton
c) Electron
d) Atom
---
### **Answers**
1. b
2. b
3. b
4. c
5. b
6. c
7. a
8. c
9. b
10. d
11. c
12. b
13. b
14. a
15. b
16. a
17. a
18. c
19. b
20. b
21. b
22. b
23. c
24. b
25. c
26. b
27. a
28. b
29. b
30. a
31. c
32. c
33. c
34. c
35. a
36. c
37. b
38. a
39. b
40. b
41. a
42. b
43. b
44. a
45. b
46. a
47. d
48. a
49. c
50. c
51. d
52. b
53. c
54. b
55. d
56. c
57. d
58. c
59. a
60. c