Atomic Foundations of Matter — Class 9 MCQs with Answers
Class 9 CBSE Science · Chapter 8
115 practice questions · 33 Easy · 42 Medium · 40 Hard · Updated
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Practise the most important Class 9 CBSE Science questions from Chapter 8, "Atomic Foundations of Matter". You get 11 timed quizzes made from 115 NCERT-based MCQs, with answers and explanations. The questions are split into 33 Easy, 42 Medium and 40 Hard. Warm up on the basics, then move on to the exam-level questions that top scorers in CBSE Board exams and the JEE & NEET foundation years get right.
To score well in "Atomic Foundations of Matter", focus on clear concepts in physics, chemistry and biology basics. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This helps you stay accurate when time is short, just as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Atomic Foundations of Matter, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 9 Science mastery score. Try the 6 sample questions below: tap an option to see the answer and a worked explanation. Sign in free to start practising.
Atomic Foundations of Matter — important questions & MCQs with answers (Class 9 Science)
6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.
0 of 6 answered
- Q1 of 6Easy
The atomic theory was proposed by:
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Answer: John Dalton
Explanation: John Dalton proposed the atomic theory in 1808, describing matter as made of indivisible atoms — this predates Rutherford's nucleus and Bohr's orbits by over a century.
- Q2 of 6Easy
The chemical formula of water is:
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Answer: H₂O
Explanation: Water's formula combines two hydrogen atoms with one oxygen atom: H₂O — the subscript 2 applies only to hydrogen, not to both elements.
- Q3 of 6Medium
Number of moles in 36 g of water (M = 18 g/mol) is:
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Answer: 2
Explanation: Moles = mass ÷ molar mass = 36 g ÷ 18 g/mol = 2 mol — dividing, not multiplying, converts grams to moles.
- Q4 of 6Medium
Assertion (A): When baking soda is added to vinegar in an open flask, the balance reading after the reaction does not match the reading before it. Reason (R): The carbon dioxide gas produced in the reaction escapes from the open flask.
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Answer: Both A and R are true and R is the correct explanation of A
Explanation: Both are true. The reading changes because the carbon dioxide formed escapes into the air; in the closed set-up with a balloon, the reading stays the same.
- Q5 of 6Hard
Molecular mass of NH₃ (N = 14, H = 1) is:
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Answer: 17 u
Explanation: Molecular mass of NH₃ = 14 + 3(1) = 17 u, counting all three hydrogens bonded to nitrogen, not just one.
- Q6 of 6Hard
Assertion (A): If 12 g of carbon combines with 32 g of oxygen to form 44 g of carbon dioxide, then 2.4 g of carbon will form 8.8 g of carbon dioxide. Reason (R): Carbon and oxygen are present in carbon dioxide in the mass ratio 3:4.
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Answer: A is true but R is false
Explanation: A is true: 2.4 × 44 ÷ 12 = 8.8 g. R is false: in carbon dioxide the ratio is 12:32 = 3:8; the ratio 3:4 is for carbon monoxide.
Atomic Foundations of Matter notes: key concepts (Class 9 Science)
Matter is made of atoms that combine in fixed whole-number ratios, which is what the laws of chemical combination assert. This chapter covers those laws, atomic and molecular masses, chemical formulae, and the mole as the chemist's counting unit.
- Law of conservation of mass
- In a chemical reaction mass is neither created nor destroyed, so the total mass of products equals that of the reactants.
- Law of constant proportions
- A pure compound always contains the same elements in the same proportion by mass, whatever its source or method of preparation.
- Dalton's atomic theory
- Matter is made of indivisible atoms; atoms of an element are identical, and compounds form when atoms combine in fixed whole-number ratios.
- Atom
- The smallest particle of an element that takes part in a chemical reaction; most atoms cannot exist independently.
- Molecule
- The smallest particle of an element or compound capable of independent existence, formed of two or more atoms held together.
- Atomicity
- The number of atoms in one molecule of an element — monoatomic for helium, diatomic for oxygen and polyatomic for phosphorus.
- Ion
- A charged particle formed when an atom or group of atoms gains or loses electrons; a cation is positive and an anion negative.
- Polyatomic ion
- A group of atoms carrying an overall charge and behaving as a single unit, such as sulphate, nitrate, carbonate and ammonium.
- Atomic mass unit
- One twelfth of the mass of a carbon-12 atom, the standard against which all atomic masses are measured.
- Molecular mass
- The sum of the atomic masses of all atoms in a molecule, expressed in atomic mass units.
- Formula unit mass
- The equivalent of molecular mass for ionic compounds, which exist as lattices rather than discrete molecules.
- Writing chemical formulae
- The valencies of the combining elements are crossed over to give the subscripts, and the formula is then reduced to its simplest ratio.
- Mole concept
- One mole is the amount of a substance containing as many particles as there are atoms in 12 g of carbon-12.
- Avogadro's number
- 6.022 × 10²³, the number of particles in one mole, which links the counting of particles to weighable masses.
- Molar mass
- The mass of one mole of a substance in grams, numerically equal to its atomic or molecular mass in atomic mass units.
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Atomic Foundations of Matter — FAQs
What are the key concepts in Class 9 Science Atomic Foundations of Matter?+
Matter is made of atoms that combine in fixed whole-number ratios, which is what the laws of chemical combination assert. This chapter covers those laws, atomic and molecular masses, chemical formulae, and the mole as the chemist's counting unit. Key ideas include Law of conservation of mass, Law of constant proportions, Dalton's atomic theory, Atom, Molecule, Atomicity.
What does Class 9 Science Chapter 8 (Atomic Foundations of Matter) cover on XamBaaz?+
It has 115 NCERT-based MCQs on "Atomic Foundations of Matter": 33 Easy, 42 Medium and 40 Hard. Together they make 11 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE Board exams and the JEE & NEET foundation years.
Are these "Atomic Foundations of Matter" questions free to practise?+
Yes. Sign in with Google to practise "Atomic Foundations of Matter" free. Full unlimited access is ₹999/year. One year from the day you pay. You stay in Class 9 till 31 March; on 1 April your account moves up to Class 10 and the rest of your year carries over. No chapter is charged separately.
How should I revise "Atomic Foundations of Matter" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 11 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Atomic Foundations of Matter" MCQs available with answers?+
Yes. 6 sample questions are on this page with answers: tap an option, or "Show answer", to see the correct option and a step-by-step explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Atomic Foundations of Matter" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Atomic Foundations of Matter (Class 9 Science)?+
The questions that matter most test Law of conservation of mass, Law of constant proportions, Dalton's atomic theory, Atom, Molecule, Atomicity. This page shows 6 solved important MCQs with answers and explanations. Sign in to practise all 115 questions on the chapter as timed quizzes.
Is there an online quiz for Atomic Foundations of Matter?+
Yes — Class 9 Science Atomic Foundations of Matter has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.
Are there question answers and extra questions for Atomic Foundations of Matter (Class 9 Science)?+
Yes. This page has 6 solved questions on Atomic Foundations of Matter, each with the correct answer and a short explanation. Sign in to practise all 115 questions on the chapter as timed quizzes.
Are there assertion–reason and case study questions for Atomic Foundations of Matter (Class 9 Science)?+
Yes. The Atomic Foundations of Matter question bank has 9 assertion–reason questions and 12 case-based (case study) questions in the CBSE board format, alongside the regular MCQs. Each comes with the answer and a worked explanation. Sign in to practise them in timed quizzes.