Class 9 Science Chapter 8 MCQs – Journey Inside the Atom provides 50 important multiple-choice questions with answers to help students revise atomic structure, subatomic particles, Rutherford’s model, Bohr’s model, electron shells, electronic configuration, atomic number, mass number, isotopes and isobars.
1. The smallest unit of an element that retains the chemical properties of that element is called:
A. Molecule
B. Atom
C. Nucleus
D. Electron
Answer: B. Atom
2. The centre of an atom is called the:
A. Electron cloud
B. Shell
C. Nucleus
D. Orbit
Answer: C. Nucleus
3. Which particles are present inside the nucleus?
A. Electrons and neutrons
B. Protons and electrons
C. Protons and neutrons
D. Only electrons
Answer: C. Protons and neutrons
4. Which subatomic particle has a negative charge?
A. Proton
B. Neutron
C. Electron
D. Nucleus
Answer: C. Electron
5. Which subatomic particle has a positive charge?
A. Electron
B. Proton
C. Neutron
D. Atom
Answer: B. Proton
6. Which subatomic particle has no electrical charge?
A. Proton
B. Electron
C. Neutron
D. Positron
Answer: C. Neutron
7. The charge on a proton is:
A. Negative
B. Positive
C. Zero
D. Variable
Answer: B. Positive
8. The charge on an electron is:
A. Positive
B. Negative
C. Zero
D. Neutral
Answer: B. Negative
9. The charge on a neutron is:
A. Positive
B. Negative
C. Zero
D. Double positive
Answer: C. Zero
10. Which scientist discovered the electron?
A. J.J. Thomson
B. Ernest Rutherford
C. James Chadwick
D. Niels Bohr
Answer: A. J.J. Thomson
11. Which scientist discovered the nucleus?
A. J.J. Thomson
B. Ernest Rutherford
C. Niels Bohr
D. Dalton
Answer: B. Ernest Rutherford
12. The neutron was discovered by:
A. J.J. Thomson
B. Rutherford
C. James Chadwick
D. Bohr
Answer: C. James Chadwick
13. Rutherford’s alpha-particle scattering experiment provided evidence for:
A. The existence of the electron only
B. The existence of a small, dense nucleus
C. The existence of neutrons only
D. The absence of empty space in atoms
Answer: B. The existence of a small, dense nucleus
14. According to Rutherford’s model, most of the atom is:
A. Filled with matter
B. Empty space
C. Filled with neutrons
D. Filled with protons
Answer: B. Empty space
15. In Rutherford’s experiment, most alpha particles:
A. Bounced straight back
B. Were absorbed by the foil
C. Passed straight through the gold foil
D. Changed into electrons
Answer: C. Passed straight through the gold foil
16. A very small number of alpha particles were deflected through large angles because:
A. Atoms are completely solid
B. They encountered the dense, positively charged nucleus
C. Electrons are positively charged
D. The gold foil was magnetic
Answer: B. They encountered the dense, positively charged nucleus
17. Rutherford’s atomic model could not explain:
A. The existence of the nucleus
B. The stability of atoms
C. The positive charge of the nucleus
D. The presence of empty space
Answer: B. The stability of atoms
18. Who proposed the model in which electrons move around the nucleus in specific energy levels?
A. Dalton
B. Thomson
C. Bohr
D. Chadwick
Answer: C. Bohr
19. According to Bohr’s model, electrons revolve around the nucleus in:
A. Random paths only
B. Fixed energy levels or shells
C. The nucleus itself
D. Straight lines
Answer: B. Fixed energy levels or shells
20. The first electron shell is represented by:
A. K
B. L
C. M
D. N
Answer: A. K
21. The second electron shell is represented by:
A. K
B. L
C. M
D. N
Answer: B. L
22. The third electron shell is represented by:
A. K
B. L
C. M
D. N
Answer: C. M
23. The maximum number of electrons that can occupy the K shell is:
A. 1
B. 2
C. 8
D. 18
Answer: B. 2
24. The maximum number of electrons that can occupy the L shell is:
A. 2
B. 4
C. 8
D. 18
Answer: C. 8
25. The maximum number of electrons that can occupy the M shell according to the shell capacity formula is:
A. 2
B. 8
C. 18
D. 32
Answer: C. 18
26. The formula for the maximum number of electrons in a shell is:
A. n²
B. 2n²
C. 2n
D. n + 2
Answer: B. 2n²
27. The electrons present in the outermost shell are called:
A. Core electrons
B. Nuclear electrons
C. Valence electrons
D. Free protons
Answer: C. Valence electrons
28. The maximum number of electrons that can be present in the outermost shell is generally:
A. 2
B. 4
C. 8
D. 18
Answer: C. 8
29. The number of protons in the nucleus of an atom is called its:
A. Mass number
B. Atomic number
C. Neutron number
D. Valency
Answer: B. Atomic number
30. Atomic number is represented by:
A. A
B. Z
C. N
D. X
Answer: B. Z
31. Mass number is equal to:
A. Number of electrons + neutrons
B. Number of protons + electrons
C. Number of protons + neutrons
D. Number of electrons only
Answer: C. Number of protons + neutrons
32. Mass number is represented by:
A. A
B. Z
C. N
D. E
Answer: A. A
33. An atom has 11 protons and 12 neutrons. Its mass number is:
A. 11
B. 12
C. 23
D. 24
Answer: C. 23
34. An atom has atomic number 8 and mass number 16. The number of neutrons is:
A. 8
B. 16
C. 24
D. 4
Answer: A. 8
35. A neutral atom has:
A. More protons than electrons
B. More electrons than protons
C. Equal numbers of protons and electrons
D. No protons
Answer: C. Equal numbers of protons and electrons
36. An atom with atomic number 17 contains how many electrons if it is neutral?
A. 7
B. 17
C. 18
D. 34
Answer: B. 17
37. The electronic configuration of an atom with atomic number 12 is:
A. 2, 8, 2
B. 2, 6, 4
C. 2, 8, 8
D. 8, 4
Answer: A. 2, 8, 2
38. The electronic configuration of oxygen (atomic number 8) is:
A. 2, 6
B. 4, 4
C. 2, 8
D. 8
Answer: A. 2, 6
39. An atom with electronic configuration 2, 8, 1 has atomic number:
A. 9
B. 10
C. 11
D. 12
Answer: C. 11
40. Isotopes are atoms of the same element having:
A. Same mass number but different atomic numbers
B. Same atomic number but different mass numbers
C. Different atomic numbers and different mass numbers
D. Same number of neutrons only
Answer: B. Same atomic number but different mass numbers
41. Which pair represents isotopes of hydrogen?
A. Hydrogen-1 and Hydrogen-2
B. Carbon-12 and Nitrogen-14
C. Sodium-23 and Magnesium-24
D. Oxygen-16 and Nitrogen-16
Answer: A. Hydrogen-1 and Hydrogen-2
42. Carbon-12 and Carbon-14 have:
A. Different atomic numbers
B. The same number of protons
C. The same number of neutrons
D. Different chemical elements
Answer: B. The same number of protons
43. The number of neutrons in carbon-14 is:
A. 6
B. 8
C. 14
D. 20
Answer: B. 8
44. Isotopes generally have similar:
A. Physical masses
B. Chemical properties
C. Numbers of neutrons
D. Mass numbers
Answer: B. Chemical properties
45. Isobars are atoms having:
A. Same atomic number but different mass numbers
B. Same mass number but different atomic numbers
C. Same number of neutrons
D. Same number of electrons only
Answer: B. Same mass number but different atomic numbers
46. Which pair represents isobars?
A. Carbon-12 and Carbon-14
B. Hydrogen-1 and Hydrogen-2
C. Argon-40 and Calcium-40
D. Chlorine-35 and Chlorine-37
Answer: C. Argon-40 and Calcium-40
47. Which of the following determines the identity of an element?
A. Number of neutrons
B. Number of electrons only
C. Number of protons
D. Mass number
Answer: C. Number of protons
48. If an atom loses one electron, it becomes:
A. A negatively charged ion
B. A positively charged ion
C. A neutron
D. A neutral molecule
Answer: B. A positively charged ion
49. If an atom gains one electron, it becomes:
A. A positively charged ion
B. A negatively charged ion
C. A proton
D. A neutron
Answer: B. A negatively charged ion
50. Which statement about an atom is correct?
A. Almost all the mass of an atom is concentrated in the nucleus
B. Electrons have positive charge
C. Neutrons are negatively charged
D. The nucleus occupies most of the volume of an atom
Answer: A. Almost all the mass of an atom is concentrated in the nucleus