Questions on Isotopes, Isobars, and Isotones
30 Multiple-Choice Questions on Isotopes, Isobars, and Isotones
1. What are isotopes?
A) Atoms with different atomic numbers but same mass number
B) Atoms with the same number of neutrons
C) Atoms with the same atomic number but different mass numbers
D) Molecules with identical formulas
E) Atoms with the same number of protons and neutrons
2. Which of the following is a pair of isotopes?
A) ⁶₃Li and ⁷₄Be
B) ¹⁴₆C and ¹²₆C
C) ²₁H and ⁴₂He
D) ¹⁶₈O and ¹⁶₇N
E) ⁴₁H and ⁴₂He
3. Isotopes of the same element have the same:
A) Number of neutrons
B) Mass number
C) Atomic number
D) Number of electrons only
E) Chemical formula
4. Isobars are atoms that have:
A) Same number of protons
B) Same number of neutrons
C) Same atomic number
D) Same mass number
E) Same number of electrons
5. Isotones are atoms that have the same number of:
A) Protons
B) Neutrons
C) Electrons
D) Mass numbers
E) Nucleons
6. Which of these pairs are isobars?
A) ⁴₁H and ⁴₂He
B) ¹⁴₇N and ¹⁴₆C
C) ¹⁵₈O and ¹⁵₇N
D) ¹⁶₈O and ¹⁶₈O
E) ⁶₃Li and ⁷₃Li
7. ¹⁵₇N and ¹⁶₈O are:
A) Isotopes
B) Isobars
C) Isotones
D) Identical
E) Not related
8. ¹²₆C and ¹³₆C are examples of:
A) Isobars
B) Ions
C) Isotones
D) Isotopes
E) Allotropes
9. Which of the following does not change among isotopes of the same element?
A) Mass number
B) Neutron number
C) Atomic number
D) Atomic mass
E) Nucleon count
10. Isobars must have:
A) Different atomic numbers
B) Same atomic numbers
C) Same number of neutrons
D) Same chemical properties
E) Equal protons and neutrons
11. Which pair are not isotopes of each other?
A) ¹H and ²H
B) ¹⁴₆C and ¹²₆C
C) ³₁H and ³₂He
D) ¹³₆C and ¹⁴₆C
E) ⁶₃Li and ⁷₃Li
12. Which of these isotopes is radioactive?
A) ¹²₆C
B) ¹⁴₆C
C) ⁶₃Li
D) ¹H
E) ¹⁶₈O
13. The number of neutrons in ¹⁴₆C is:
A) 6
B) 8
C) 14
D) 12
E) 10
14. Isotones share the same number of:
A) Electrons
B) Nucleons
C) Protons
D) Neutrons
E) Mass number
15. What are the number of neutrons in ³₁H and ⁴₂He respectively?
A) 2 and 2
B) 2 and 1
C) 1 and 2
D) 2 and 4
E) 3 and 2
16. Which of the following are both isotopes and isotones?
A) ⁶₃Li and ⁷₃Li
B) ¹⁴₇N and ¹⁵₈O
C) ³₁H and ³₂He
D) ¹²₆C and ¹⁴₇N
E) None of the above
17. Which of the following statements is true?
A) Isobars always have similar chemical properties
B) Isotopes have different numbers of protons
C) Isotones have same number of neutrons
D) Isobars are always unstable
E) Isotopes cannot be of the same element
18. Isobars differ in their:
A) Atomic number
B) Mass number
C) Number of nucleons
D) Number of neutrons
E) Both A and D
19. Which of the following statements is incorrect?
A) Isotopes have the same atomic number
B) Isobars have the same number of nucleons
C) Isotones have the same number of neutrons
D) Isotopes are chemically different elements
E) Isobars have different proton numbers
20. Which of these are isotones?
A) ¹³₆C and ¹⁴₇N
B) ¹⁵₇N and ¹⁶₈O
C) ⁶₃Li and ⁷₄Be
D) ¹²₆C and ¹⁴₆C
E) A and B
21. Which of the following pairs have the same number of neutrons?
A) ⁹₄Be and ¹⁰₅B
B) ¹⁴₆C and ¹⁴₇N
C) ⁷₃Li and ⁸₄Be
D) ¹⁶₈O and ¹⁷₈O
E) ¹²₆C and ¹³₆C
22. Which of the following pairs are isobars?
A) ¹⁴₇N and ¹⁴₆C
B) ¹³₆C and ¹⁴₇N
C) ⁴₂He and ⁴₁H
D) All of the above
E) None of the above
23. Which property is usually identical for isotopes of an element?
A) Atomic mass
B) Mass number
C) Nuclear stability
D) Chemical properties
E) Number of neutrons
24. What distinguishes isotones from isotopes?
A) Different mass number
B) Same atomic number
C) Same number of neutrons
D) Same number of protons
E) Same atomic mass
25. What is the relationship between ¹⁴₇N and ¹⁵₈O?
A) Isotopes
B) Isobars
C) Isotones
D) Identical
E) Isomers
26. Which of these is not a property of isobars?
A) Same atomic number
B) Different atomic number
C) Same mass number
D) May be different elements
E) Same nucleon count
27. Which of the following is the correct pair of isotones?
A) ¹³₆C and ¹⁴₆C
B) ⁷₃Li and ⁸₃Li
C) ⁷₃Li and ⁸₄Be
D) ¹⁵₇N and ¹⁶₈O
E) None of the above
28. Which pair is not correctly classified?
A) Isotopes – ¹²₆C and ¹³₆C
B) Isobars – ⁴₁H and ⁴₂He
C) Isotones – ¹⁵₇N and ¹⁶₈O
D) Isotopes – ⁶₃Li and ⁷₄Be
E) Isobars – ¹⁴₇N and ¹⁴₆C
29. What do isotopes have in common?
A) Same number of neutrons
B) Same number of nucleons
C) Same number of protons
D) Same mass number
E) Same atomic mass
30. What is the number of neutrons in ¹⁷₈O?
A) 8
B) 9
C) 10
D) 17
E) 7
Answer Key with Explanations
1. C – Same atomic number (same protons), different mass numbers (different neutrons).
2. B – Carbon-14 and Carbon-12 are isotopes (same atomic number, different masses).
3. C – Isotopes have same atomic number.
4. D – Isobars have same mass number, different atomic numbers.
5. B – Isotones = same number of neutrons.
6. B – 14N and 14C = same mass number → isobars.
7. C – ¹⁵₇N and ¹⁶₈O both have 8 neutrons.
8. D – Carbon-12 and Carbon-13 = isotopes.
9. C – Atomic number remains constant across isotopes.
10. A – Isobars = same mass number, different atomic numbers.
11. C – ³₁H and ³₂He are not isotopes (different atomic numbers).
12. B – ¹⁴₆C is radioactive.
13. B – 14 (mass) – 6 (protons) = 8 neutrons.
14. D – Isotones = same number of neutrons.
15. C – 3H: 2 neutrons, 4He: 2 neutrons.
16. E – No pair satisfies both conditions.
17. C – Isotones = same neutrons.
18. E – Isobars differ in both atomic number and neutrons.
19. D – Isotopes are chemically similar, not different.
20. E – Both A and B are correct.
21. A – Both have 5 neutrons.
22. D – All are isobars (same mass number, different elements).
23. D – Same chemical properties.
24. C – Isotones = same neutrons, different atomic number.
25. C – ¹⁵₇N and ¹⁶₈O = 8 neutrons.
26. A – Isobars do not have same atomic number.
27. D – Both have 8 neutrons.
28. D – ⁶₃Li and ⁷₄Be are not isotopes (different atomic number).
29. C – Isotopes = same protons.
30. B – 17 – 8 = 9 neutrons.
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