1. The smallest particle of an element that retains its chemical properties is called a:
A) Molecule
B) Atom
C) Compound
D) Ion
2. Who proposed the nuclear model of the atom?
A) Ernest Rutherford
B) John Dalton
C) J. J. Thomson
D) Niels Bohr
3. Which subatomic particle carries a negative charge?
A) Proton
B) Neutron
C) Alpha particle
D) Electron
4. The nucleus of an atom contains:
A) Electrons only
B) Electrons and neutrons
C) Protons and neutrons
D) Protons only
5. The atomic number of an element is equal to the number of:
A) Neutrons
B) Protons
C) Nucleons
D) Shells
6. The mass number of an atom is the total number of:
A) Protons and neutrons
B) Electrons and protons
C) Electrons only
D) Neutrons only
7. An atom is electrically neutral because:
A) It has no nucleus
B) It contains neutrons only
C) It has equal protons and neutrons
D) It has equal numbers of protons and electrons
8. Which scientist discovered the electron?
A) James Chadwick
B) Ernest Rutherford
C) J. J. Thomson
D) Niels Bohr
9. Which particle has approximately the same mass as a proton but no charge?
A) Electron
B) Neutron
C) Positron
D) Photon
10. The maximum number of electrons that can be accommodated in the first shell (K-shell) is:
A) 2
B) 8
C) 18
D) 32
11. Isotopes of an element have the same:
A) Mass number
B) Number of neutrons
C) Atomic mass
D) Atomic number
12. The scientist who discovered the neutron was:
A) Dalton
B) Bohr
C) James Chadwick
D) Thomson
13. Which particle is responsible for most of the mass of an atom?
A) Protons and neutrons
B) Electrons only
C) Protons only
D) Electrons and photons
14. The electron revolves around the nucleus in:
A) Molecules
B) Energy levels or shells
C) Compounds
D) Chemical bonds
15. An atom with atomic number 8 contains:
A) 8 neutrons only
B) 8 protons and 10 electrons
C) 16 protons
D) 8 protons and 8 electrons
16. Which model introduced fixed energy levels for electrons?
A) Bohr Model
B) Dalton Model
C) Thomson Model
D) Rutherford Model
17. The symbol Z is commonly used to represent the:
A) Mass number
B) Atomic mass
C) Atomic number
D) Valency
18. Which scientist proposed the “plum pudding” model of the atom?
A) Ernest Rutherford
B) J. J. Thomson
C) Niels Bohr
D) James Chadwick
19. The number of neutrons in an atom is calculated by:
A) Atomic number + Mass number
B) Number of electrons + Protons
C) Mass number × Atomic number
D) Mass number − Atomic number
20. Which subatomic particle determines the identity of an element?
A) Proton
B) Electron
C) Neutron
D) Photon
21. The atomic number of sodium is 11. A neutral sodium atom contains:
A) 11 neutrons
B) 22 electrons
C) 11 electrons
D) 23 electrons
22. Which shell can accommodate a maximum of 8 electrons?
A) K-shell
B) L-shell
C) N-shell
D) O-shell
23. Atoms of the same element having different numbers of neutrons are called:
A) Isotopes
B) Isobars
C) Ions
D) Molecules
24. Which particle is located outside the nucleus?
A) Proton
B) Neutron
C) Nucleon
D) Electron
25. The mass of an electron is:
A) Equal to a proton
B) Greater than a neutron
C) Negligible compared to protons and neutrons
D) Twice that of a proton
26. Which of the following particles has a positive charge?
A) Proton
B) Electron
C) Neutron
D) Gamma ray
27. An isotope of carbon with mass number 14 has:
A) 14 protons
B) 8 neutrons
C) 14 electrons only
D) 6 neutrons
28. Which statement about neutrons is correct?
A) They carry a positive charge
B) They orbit the nucleus
C) They have a negative charge
D) They are electrically neutral and found in the nucleus
29. The electronic configuration of oxygen (atomic number 8) is:
A) 2,6
B) 2,8
C) 4,4
D) 8
30. Which model suggested that electrons revolve around the nucleus in fixed energy levels?
A) Dalton’s Model
B) Thomson’s Model
C) Bohr’s Model
D) Democritus’ Model
31. The nucleus occupies:
A) Almost the entire atom
B) A very small central region of the atom
C) The outermost shell only
D) Half of the atom’s volume
32. The sum of protons and neutrons in an atom is called its:
A) Atomic number
B) Valency
C) Electronic configuration
D) Mass number
33. Hydrogen-1 contains:
A) 1 proton and 0 neutrons
B) 1 proton and 1 neutron
C) 2 protons
D) 2 neutrons
34. Which statement is true for a neutral atom?
A) Protons are fewer than electrons
B) Neutrons equal electrons in every atom
C) Number of protons equals number of electrons
D) Number of neutrons always equals protons
35. Which subatomic particle contributes negligibly to the mass of an atom?
A) Proton
B) Electron
C) Neutron
D) Nucleus
36. The electronic configuration of sodium (atomic number 11) is:
A) 2,9
B) 8,3
C) 2,8,2
D) 2,8,1
37. Which scientist proposed that atoms are indivisible solid spheres?
A) John Dalton
B) Niels Bohr
C) James Chadwick
D) Ernest Rutherford
38. An atom of chlorine has atomic number 17. How many protons does it contain?
A) 18
B) 35
C) 17
D) 16
39. Which shell is filled first when electrons are arranged around the nucleus?
A) L-shell
B) K-shell
C) M-shell
D) N-shell
40. Which pair correctly represents the charges of a proton and an electron?
A) +1 and −1
B) −1 and +1
C) 0 and +1
D) +2 and −2
41. Which statement about isotopes is correct?
A) They have different atomic numbers.
B) They have different numbers of protons.
C) They belong to different elements.
D) They have the same atomic number but different mass numbers.
42. The maximum number of electrons that can occupy the L-shell is:
A) 2
B) 8
C) 18
D) 32
43. Which of the following has no electrical charge?
A) Electron
B) Proton
C) Neutron
D) Positron
44. The atomic number of magnesium is 12. Its electronic configuration is:
A) 2,8,2
B) 2,6,4
C) 2,10
D) 8,4
45. The nucleus of an atom is positively charged because it contains:
A) Electrons only
B) Neutrons only
C) Equal electrons and protons
D) Protons
46. Which isotope of hydrogen contains one proton and one neutron?
A) Protium
B) Deuterium
C) Tritium-free hydrogen
D) Helium
47. If an atom has 15 protons and 16 neutrons, its mass number is:
A) 31
B) 15
C) 16
D) 1
48. The arrangement of electrons in different shells of an atom is called:
A) Atomic mass
B) Atomic structure
C) Electronic configuration
D) Mass spectrum
49. Which statement about electrons is correct?
A) They are found inside the nucleus.
B) They have a positive charge.
C) They contribute most of the atomic mass.
D) They occupy shells around the nucleus.
50. The main objective of Chapter 3 “Structure of Atoms” is to help students understand:
A) Chemical reactions only
B) Atomic models, subatomic particles, isotopes, atomic number, mass number, and electronic configuration
C) Laboratory apparatus only
D) Organic compounds only