SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs (2026–27) – Assam Eduverse
The SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs (2026–27) are prepared strictly according to the latest ASSEB syllabus and updated board examination pattern. These SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs include important objective questions, numerical-based MCQs, and conceptual practice sets designed to strengthen board exam preparation.
Prepared by subject experts of Assam Eduverse, these seba class 9 science chapter 3 mcqs focus on important concepts such as laws of chemical combination, Dalton’s atomic theory, atomic mass, molecular mass, mole concept, valency, and writing chemical formulae. Practicing these atoms and molecules mcqs class 9 seba and assam board class 9 science objective questions improves conceptual clarity and problem-solving accuracy.
Regular revision of these ASSEB Class 9 Science Important MCQs ensures strong preparation for the 2026–27 board examination and enhances scoring potential in MCQ-based assessments.
SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs – ASSEB 2026–27 Board Exam Practice
Table of Contents
Q1. Who proposed that matter is made up of indivisible particles called atoms?
a) Lavoisier
b) John Dalton
c) Proust
d) Berzilius
Answer: b) John Dalton
Q2. The law which states that mass can neither be created nor destroyed in a chemical reaction is called:
a) Law of definite proportions
b) Law of multiple proportions
c) Law of conservation of mass
d) Atomic theory
Answer: c) Law of conservation of mass
Q3. The law of constant proportions was stated by:
a) Dalton
b) Lavoisier
c) Proust
d) Democritus
Answer: c) Proust
Q4. In water, the ratio of mass of hydrogen to oxygen is:
a) 1 : 2
b) 2 : 1
c) 1 : 8
d) 8 : 1
Answer: c) 1 : 8
Q5. Atoms of different elements differ in:
a) Colour only
b) Mass and chemical properties
c) Size only
d) Shape only
Answer: b) Mass and chemical properties
Q6. Atomic radius is measured in:
a) metre
b) centimetre
c) nanometre
d) millimetre
Answer: c) nanometre
Q7. 1 nanometre is equal to:
a) 10⁻⁶ m
b) 10⁻⁹ m
c) 10⁻³ m
d) 10⁻¹² m
Answer: b) 10⁻⁹ m
Q8. Which of the following is a monoatomic molecule?
a) Oxygen
b) Nitrogen
c) Argon
d) Chlorine
Answer: c) Argon
Q9. The number of atoms present in one molecule of oxygen (O₂) is:
a) 1
b) 2
c) 3
d) 4
Answer: b) 2
Q10. The atomicity of phosphorus is:
a) 1
b) 2
c) 4
d) 8
Answer: c) 4
Q11. Which of the following is a polyatomic ion?
a) Na⁺
b) Cl⁻
c) OH⁻
d) H⁺
Answer: c) OH⁻
Q12. The valency of oxygen is:
a) 1
b) 2
c) 3
d) 4
Answer: b) 2
Q13. The chemical formula of calcium oxide is:
a) Ca₂O
b) CaO₂
c) CaO
d) Ca₂O₂
Answer: c) CaO
Q14. The chemical formula of aluminium oxide is:
a) AlO
b) Al₂O₃
c) Al₃O₂
d) AlO₃
Answer: b) Al₂O₃
Q15. The molecular mass of water (H₂O) is:
a) 16 u
b) 17 u
c) 18 u
d) 20 u
Answer: c) 18 u
Q16. The formula unit mass of NaCl is:
a) 23 u
b) 35.5 u
c) 58.5 u
d) 46 u
Answer: c) 58.5 u
Q17. One mole of any substance contains:
a) 6.022 × 10²³ particles
b) 6.022 × 10²² particles
c) 6.022 × 10²⁴ particles
d) 3.011 × 10²³ particles
Answer: a) 6.022 × 10²³ particles
Q18. The SI unit of amount of substance is:
a) gram
b) kilogram
c) mole
d) atomic mass unit
Answer: c) mole
Q19. The molar mass of hydrogen atom is:
a) 1 g
b) 2 g
c) 1 u
d) 2 u
Answer: a) 1 g
Q20. The formula of ammonium sulphate is:
a) NH₄SO₄
b) (NH₄)₂SO₄
c) NH₄₂SO₄
d) NH₄(SO₄)₂
Answer: b) (NH₄)₂SO₄
Q21. Assertion: Mass remains constant during a chemical reaction.
Reason: Atoms are neither created nor destroyed in a chemical reaction.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q22. Assertion: Water always contains hydrogen and oxygen in the ratio 1:8 by mass.
Reason: Elements in a compound are present in definite proportions by mass.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q23. Assertion: Atoms of the same element have identical chemical properties.
Reason: Atoms of the same element have identical mass.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: b) Both A and R are true but R is not the correct explanation of A
Q24. Assertion: Argon is monoatomic.
Reason: Argon molecule contains only one atom.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q25. Assertion: One mole of oxygen molecules contains 6.022 × 10²³ molecules.
Reason: Mole is the SI unit of mass.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: c) A is true but R is false
Q26. Assertion: Atomic mass unit is defined using carbon-12 isotope.
Reason: One atomic mass unit is equal to one-twelfth the mass of one carbon-12 atom.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q27. Assertion: Metals and some elements like carbon do not have simple molecular structures.
Reason: They consist of a very large and indefinite number of atoms bonded together.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q28. Assertion: The formula of calcium hydroxide is Ca(OH)₂.
Reason: Brackets are used when more than one polyatomic ion is present.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q29. Assertion: Molecular mass is the sum of atomic masses of all atoms in a molecule.
Reason: Molecular mass is expressed in atomic mass unit (u).
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: b) Both A and R are true but R is not the correct explanation of A
Q30. Assertion: In ionic compounds, charges on ions must balance.
Reason: Overall structure of an ionic compound must be neutral.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Answer: a) Both A and R are true and R is the correct explanation of A
Q31. Which of the following statements are correct about Dalton’s atomic theory?
i) Atoms are indivisible.
ii) Atoms can be created in a chemical reaction.
iii) Atoms combine in simple whole number ratios.
a) i and iii only
b) i and ii only
c) ii and iii only
d) i, ii and iii
Answer: a) i and iii only
Q32. Which of the following are diatomic molecules?
i) O₂
ii) N₂
iii) Ar
a) i and ii only
b) ii and iii only
c) i and iii only
d) i, ii and iii
Answer: a) i and ii only
Q33. Which of the following are polyatomic ions?
i) SO₄²⁻
ii) NH₄⁺
iii) Cl⁻
a) i and ii only
b) ii and iii only
c) i and iii only
d) i, ii and iii
Answer: a) i and ii only
Q34. Which of the following follow the law of definite proportions?
i) Mixture
ii) Compound
iii) Solution
iv) Alloy
a) ii only
b) i and ii
c) ii and iii
d) i, ii, iii and iv
Answer: a) ii only
Q35. Which of the following represents Avogadro number?
i) 6.022 × 10²³
ii) 6.022 × 10²²
iii) 3.011 × 10²³
iv) 1 × 10²³
a) i only
b) i and ii
c) ii and iii
d) i, ii, iii and iv
Answer: a) i only
Q36. Which of the following is a binary compound?
i) NaCl
ii) NH₄Cl
iii) Na₂SO₄
iv) Ca(OH)₂
a) i only
b) i and ii
c) ii and iii
d) i, ii, iii and iv
Answer: a) i only
Q37. Which of the following formulae are correct?
i) MgCl₂
ii) Na₂CO₃
iii) CaCl
a) i and ii only
b) ii and iii only
c) i and iii only
d) i, ii and iii
Answer: a) i and ii only
Q38. Molar mass of oxygen molecule (O₂) is:
a) 16 g
b) 32 g
c) 8 g
d) 2 g
Answer: b) 32 g
Q39. One mole of carbon atoms weighs:
a) 6 g
b) 12 g
c) 18 g
d) 24 g
Answer: b) 12 g
Q40. Which of the following is tetra-atomic?
a) Nitrogen
b) Oxygen
c) Phosphorus
d) Chlorine
Answer: c) Phosphorus
Q41. Match the following:
| Column A | Column B |
|---|---|
| 1) Law of conservation of mass | a) 6.022 × 10²³ particles |
| 2) Law of definite proportions | b) 1/12th mass of carbon-12 |
| 3) Atomic mass unit | c) Mass remains constant |
| 4) Mole | d) Fixed proportion by mass |
a) 1-c, 2-d, 3-b, 4-a
b) 1-d, 2-c, 3-a, 4-b
c) 1-c, 2-b, 3-d, 4-a
d) 1-a, 2-d, 3-b, 4-c
Answer: a) 1-c, 2-d, 3-b, 4-a
Q42. Match the following:
| Column A | Column B |
|---|---|
| 1) H₂O | a) Ozone |
| 2) NH₃ | b) Ammonia |
| 3) CO₂ | c) Water |
| 4) O₃ | d) Carbon dioxide |
a) 1-c, 2-b, 3-d, 4-a
b) 1-b, 2-c, 3-a, 4-d
c) 1-c, 2-d, 3-b, 4-a
d) 1-a, 2-b, 3-c, 4-d
Answer: a) 1-c, 2-b, 3-d, 4-a
Q43. Match the following:
| Column A | Column B |
|---|---|
| 1) Na⁺ | a) Cation |
| 2) Cl⁻ | b) Anion |
| 3) SO₄²⁻ | c) Polyatomic ion |
| 4) NH₄⁺ | d) Positively charged ion |
a) 1-a, 2-b, 3-c, 4-d
b) 1-d, 2-b, 3-c, 4-a
c) 1-a, 2-c, 3-b, 4-d
d) 1-d, 2-a, 3-c, 4-b
Answer: b) 1-d, 2-b, 3-c, 4-a
Q44. Match the following atomic masses:
| Column A | Column B |
|---|---|
| 1) Hydrogen | a) 12 u |
| 2) Oxygen | b) 1 u |
| 3) Nitrogen | c) 16 u |
| 4) Carbon | d) 14 u |
a) 1-b, 2-c, 3-d, 4-a
b) 1-a, 2-b, 3-c, 4-d
c) 1-b, 2-d, 3-c, 4-a
d) 1-c, 2-b, 3-a, 4-d
Answer: a) 1-b, 2-c, 3-d, 4-a
SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs (2026–27) Important Objective Questions
The SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs are prepared strictly as per the latest ASSEB syllabus 2026–27. These SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs include conceptual objective questions, numerical MCQs, and board-oriented practice sets.
Students preparing for the board examination should regularly practice SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs. These seba class 9 science chapter 3 mcqs cover key topics such as laws of conservation of mass, law of constant proportions, Dalton’s atomic theory, atomic mass calculation, molecular mass determination, and the mole concept.
The atoms and molecules mcqs class 9 seba provided here are prepared by subject experts to ensure complete alignment with the latest exam pattern. These ASSEB class 9 science important MCQs help students master writing chemical formulae, understanding valency, and solving mole-based numerical problems.
Regular revision of SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs along with assam board class 9 science objective questions improves accuracy, conceptual clarity, and scoring performance in the 2026–27 ASSEB board examination.
Frequently Asked Questions (FAQ)
1. Are these SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs based on the latest syllabus?
Yes, these SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs follow the latest ASSEB syllabus for 2026–27.
2. Are these seba class 9 science chapter 3 mcqs helpful for board exam preparation?
Yes, these seba class 9 science chapter 3 mcqs are designed according to the latest board exam pattern.
3. Do these atoms and molecules mcqs class 9 seba include numerical problems?
Yes, these atoms and molecules mcqs class 9 seba include numerical questions based on mole concept and atomic mass.
4. Who prepared these ASSEB class 9 science important MCQs?
These ASSEB class 9 science important MCQs are prepared by subject experts of Assam Eduverse.
5. Are assam board class 9 science objective questions from this chapter frequently asked?
Yes, important assam board class 9 science objective questions from Atoms and Molecules are frequently asked in exams.
6. Which important topics are covered in Chapter 3 MCQs?
Topics include Dalton’s atomic theory, laws of chemical combination, mole concept, valency, atomic mass, and molecular mass.
7. Can regular practice of SEBA Class 9 Science Chapter 3 Atoms and Molecules MCQs improve scores?
Yes, regular practice improves conceptual clarity, numerical accuracy, and scoring performance in the board examination.
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