Class 9 • Chemistry • Chapter 3
Atoms and Molecules
True & False Quiz
Atom. Mole. Formula.
✓True
✗False
25
Questions
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Ch.3
Chapter
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IX
Class
Why True & False for Atoms and Molecules?
How this format sharpens your conceptual clarity
🔵 Atoms and Molecules introduces the quantitative language of chemistry — atomic masses, moles, and chemical formulae that appear in every subsequent chapter.
✅ T/F tests laws of chemical combination, atomicity, valency, formulae writing, and mole concept calculations.
🎯 Avogadro's number is 6.022 × 10²³ per mole — it applies to atoms, molecules, ions, and any elementary entity, NOT just molecules.
📋
Read each statement carefully. Click True or False — instant feedback with explanation appears. Submit anytime; unattempted questions are marked Skipped.
Q 1
Atoms are indivisible and indestructible.
Q 2
A molecule of water contains two hydrogen atoms and one oxygen atom.
Q 3
Chemical symbols are always represented by one or two letters.
Q 4
Oxygen is a monatomic molecule.
Q 5
Law of conservation of mass states that mass can be created or destroyed.
Q 6
Law of constant proportions is also known as the law of definite proportions.
Q 7
Dalton’s atomic theory was the first to propose that atoms combine in simple ratios to form compounds.
Q 8
The atomic mass unit (amu) is defined based on hydrogen.
Q 9
Sodium's chemical symbol is So.
Q 10
HCl represents hydrochloric acid.
Q 11
The number of protons and electrons are equal in a neutral atom.
Q 12
\(\mathrm{O_2}\) represents a polyatomic molecule.
Q 13
One mole of any substance contains Avogadro’s number of particles.
Q 14
Gram molecular mass is the mass of one molecule in grams.
Q 15
Chemical formula of ammonia is \(\mathrm{NH_3}\).
Q 16
Atoms of the same element can have different masses.
Q 17
Hydrogen and oxygen combine to form water in a 2:1 mass ratio.
Q 18
The symbol for chlorine is Cl.
Q 19
All molecules are compounds.
Q 20
The valency of hydrogen is one.
Q 21
Atoms can exist freely in nature.
Q 22
Ions are electrically neutral.
Q 23
\(\mathrm{SO_4^{2-} is a polyatomic ion.
Q 24
Isotopes have the same atomic number but different mass numbers.
Q 25
Law of multiple proportions applies to any two elements combining to form more than one compound.
Key Takeaways — Atoms and Molecules
Core facts for CBSE Boards & exams
1
Law of Conservation of Mass: mass of reactants = mass of products.
2
Law of Constant Proportions: a compound always contains elements in a fixed mass ratio.
3
Atomic mass unit (amu): 1/12th the mass of a C-12 atom; H = 1 amu, O = 16 amu.
4
Mole = 6.022 × 10²³ particles (Avogadro's Number); molar mass = atomic/molecular mass in grams.
5
Atomicity: number of atoms in one molecule (O₂ = 2, O₃ = 3, P₄ = 4, S₈ = 8).
6
Valency determines how many bonds an atom forms; it guides writing chemical formulae.