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Atoms and Molecules — Class 9 CBSE Science MCQs with Solutions
Free Class 9 CBSE Science Atoms and Molecules MCQs with step-by-step solutions. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — easy
Law of Conservation of Mass was given by which French chemist?
A. John Dalton
B. Antoine Lavoisier ✓ Correct
C. Joseph Proust
D. J.J. Thomson
Solution: Lavoisier established that mass is neither created nor destroyed in a chemical reaction.
Q2 — easy
Law of Constant Proportions states that in a chemical substance, elements are always present in:
A. Random ratios
B. Definite proportions by mass ✓ Correct
C. Equal volume ratios
D. Variable mass ratios
Solution: Proust stated elements combine in fixed mass proportions (e.g. H:O in water = 1:8).
Q3 — easy
Relative atomic mass of carbon-12 isotope is assigned a standard value of:
A. 1 u
B. 12 u ✓ Correct
C. 16 u
D. 10 u
Solution: 1/12th of Carbon-12 atom mass is taken as 1 atomic mass unit (u).
Q4 — easy
Chemical formula of Aluminium Oxide is:
A. AlO
B. Al₂O₃ ✓ Correct
C. Al₃O₂
D. AlO₂
Solution: Valency of Al = 3+, O = 2−; criss-cross gives Al₂O₃.
Q5 — easy
Atomicity of Ozone molecule (O₃) is:
A. 1
B. 2
C. 3 ✓ Correct
D. 4
Solution: Ozone contains 3 oxygen atoms, so atomicity = 3.
Q6 — easy
Chemical formula of Calcium Carbonate is:
A. CaCO₃ ✓ Correct
B. Ca₂CO₃
C. CaHCO₃
D. CaSO₄
Solution: Ca²⁺ and CO₃²⁻ combine to form CaCO₃.
Q7 — easy
Molecular mass of water (H₂O) is: (H = 1 u, O = 16 u)
A. 17 u
B. 18 u ✓ Correct
C. 20 u
D. 32 u
Solution: 2(1) + 16 = 18 u.
Q8 — easy
Formula unit mass of Sodium Chloride (NaCl) is: (Na = 23 u, Cl = 35.5 u)
A. 58.5 u ✓ Correct
B. 58 u
C. 60 u
D. 35.5 u
Solution: 23 + 35.5 = 58.5 u.
Q9 — easy
A polyatomic ion carrying a net negative charge is called a polyatomic:
A. Cation
B. Anion ✓ Correct
C. Molecule
D. Isotope
Solution: Negatively charged species are anions.
Q10 — easy
Valency of Carbon atom in organic compounds is:
A. 1
B. 2
C. 3
D. 4 ✓ Correct
Solution: Carbon has 4 valence electrons and is tetravalent.
Q11 — easy
Ammonium ion is represented by chemical formula:
A. NH₃
B. NH₄⁺ ✓ Correct
C. NO₃⁻
D. NO₂⁻
Solution: Ammonium polyatomic cation is NH₄⁺.
Q12 — easy
Sulphate ion carries a valency charge of:
A. 1−
B. 2− (SO₄²⁻) ✓ Correct
C. 3−
D. 1+
Solution: Sulphate ion is SO₄²⁻.
Q13 — easy
Who proposed the atomic theory stating that all matter is made of indivisible atoms?
A. J.J. Thomson
B. John Dalton ✓ Correct
C. Rutherford
D. Bohr
Solution: Dalton proposed Dalton's Atomic Theory in 1808.
Q14 — easy
A molecule containing two identical atoms bound together (e.g. O₂, N₂) is:
A. Monatomic
B. Diatomic ✓ Correct
C. Triatomic
D. Polyatomic
Solution: Diatomic molecules consist of two bound atoms.
Q15 — easy
Quick lime is chemically known as:
A. Calcium Carbonate
B. Calcium Oxide (CaO) ✓ Correct
C. Calcium Hydroxide
D. Calcium Chloride
Solution: Quick lime = Calcium Oxide (CaO).