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CBSE Class 9  >  Class 9 Test  >  Science New NCERT 2026-27 (New Syllabus)  >  Test: Atomic Foundations of Matter - 2 - Class 9 MCQ

Atomic Foundations of Matter - 2 - Free MCQ Practice Test with solutions,


MCQ Practice Test & Solutions: Test: Atomic Foundations of Matter - 2 (15 Questions)

You can prepare effectively for Class 9 Science Class 9 New NCERT 2026-27 (New Syllabus) with this dedicated MCQ Practice Test (available with solutions) on the important topic of "Test: Atomic Foundations of Matter - 2". These 15 questions have been designed by the experts with the latest curriculum of Class 9 2026, to help you master the concept.

Test Highlights:

  • - Format: Multiple Choice Questions (MCQ)
  • - Duration: 15 minutes
  • - Number of Questions: 15

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Test: Atomic Foundations of Matter - 2 - Question 1
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The formula unit mass of Na₂O is: (Na = 23 u, O = 16 u)

Detailed Solution: Question 1

Formula unit mass of Na₂O = (atomic mass of Na × 2) + (atomic mass of O × 1) = (23 × 2) + (16 × 1) = 46 + 16 = 62 u. Note: Ionic compounds like Na₂O do not form molecules; instead we calculate formula unit mass based on the simplest ratio of ions.

Test: Atomic Foundations of Matter - 2 - Question 2
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Which of the following correctly describes a polyatomic ion?

Detailed Solution: Question 2

A polyatomic ion consists of two or more atoms covalently bonded together that carry an overall positive or negative charge and act as a single unit. Examples include SO₄²⁻ (sulphate), NO₃⁻ (nitrate), OH⁻ (hydroxide), and NH₄⁺ (ammonium). Their names generally do not end with '-ide'.

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Test: Atomic Foundations of Matter - 2 - Question 3
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What is the correct chemical formula of magnesium hydroxide?

Detailed Solution: Question 3

Magnesium ion (Mg²⁺) has charge 2+ and hydroxide ion (OH⁻) has charge 1−. Using the criss-cross method, subscript of Mg = 1 and subscript of OH = 2, giving Mg(OH)₂. Brackets are used around the polyatomic hydroxide ion because there are two of them. The compound is electrically neutral: 1 × 2+ = 2+ and 2 × 1− = 2−.

Test: Atomic Foundations of Matter - 2 - Question 4
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In the verification of the Law of Conservation of Mass using Na₂SO₄ and BaCl₂, what white precipitate is formed?

Detailed Solution: Question 4

When sodium sulfate (Na₂SO₄) solution is mixed with barium chloride (BaCl₂) solution, the reaction is: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl. A white precipitate of barium sulfate (BaSO₄) is formed. Since no gas is produced, this reaction can verify the Law of Conservation of Mass even in an open system.

Test: Atomic Foundations of Matter - 2 - Question 5
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Atoms with less than 4 valence electrons tend to:

Detailed Solution: Question 5

Atoms that have fewer than 4 electrons in their valence shell find it easier to lose those electrons rather than gain many more to complete the octet. By losing electrons, they form positively charged ions called cations. For example, sodium has 1 valence electron and loses it to form Na⁺, and magnesium has 2 valence electrons and loses both to form Mg²⁺.

Test: Atomic Foundations of Matter - 2 - Question 6
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What is the correct chemical formula of aluminium sulfate?

Detailed Solution: Question 6

Aluminium ion (Al³⁺) has charge 3+ and sulphate ion (SO₄²⁻) has charge 2−. Using the criss-cross method, subscript of Al = 2 (from SO₄'s charge of 2) and subscript of SO₄ = 3 (from Al's charge of 3), giving Al₂(SO₄)₃. Verification: 2 × 3+ = 6+ and 3 × 2− = 6−, making the compound electrically neutral.

Test: Atomic Foundations of Matter - 2 - Question 7
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Which of the following statements about covalent compounds is CORRECT?

Detailed Solution: Question 7

Covalent compounds such as sugar and camphor generally do not conduct electricity because they do not dissociate into ions in solution — there are no free charge carriers. For example, a sugar solution does not conduct electricity. This is in contrast to ionic compounds, which conduct electricity when dissolved in water or in molten state due to the presence of free-moving ions.

Test: Atomic Foundations of Matter - 2 - Question 8
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What is the formula unit mass of Ca(NO₃)₂? (Ca = 40 u, N = 14 u, O = 16 u)

Detailed Solution: Question 8

Formula unit mass of Ca(NO₃)₂ = mass of Ca + 2 × mass of NO₃ = 40 + 2 × (14 + 3 × 16) = 40 + 2 × (14 + 48) = 40 + 2 × 62 = 40 + 124 = 164 u. There are 2 nitrate ions, each containing 1 nitrogen and 3 oxygen atoms.

Test: Atomic Foundations of Matter - 2 - Question 9
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The IUPAC name of CS₂ is:

Detailed Solution: Question 9

CS₂ contains 1 carbon atom and 2 sulfur atoms. As per the naming rules for covalent compounds, 'mono' is not used for the first element, so carbon keeps its full name. 'Di' is placed before 'sulfide' to indicate 2 sulfur atoms, and the second element always ends with '-ide'. Therefore, CS₂ is correctly named carbon disulfide.

Test: Atomic Foundations of Matter - 2 - Question 10
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Which of the following best describes an ionic bond?

Detailed Solution: Question 10

An ionic bond is formed when one atom (usually a metal) loses electrons to become a cation and another atom (usually a non-metal) gains those electrons to become an anion. The resulting oppositely charged ions attract each other due to electrostatic force of attraction, forming the ionic bond. For example, Na loses an electron to become Na⁺ and Cl gains that electron to become Cl⁻, together forming NaCl.

Test: Atomic Foundations of Matter - 2 - Question 11
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In the formation of HCl, hydrogen and chlorine atoms:

Detailed Solution: Question 11

Hydrogen has 1 valence electron (needs 1 more for duplet) and chlorine has 7 valence electrons (needs 1 more for octet). Both atoms share one electron each — hydrogen contributes 1 electron and chlorine contributes 1 electron — forming a shared pair. This forms a single covalent bond, and the molecule HCl is represented as H−Cl.

Test: Atomic Foundations of Matter - 2 - Question 12
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Which of the following correctly states a limitation of Dalton's Atomic Theory?

Detailed Solution: Question 12

One of the major limitations of Dalton's Atomic Theory is his claim that atoms are indivisible. However, modern science has discovered that atoms are made up of subatomic particles — electrons, protons, and neutrons. Despite this limitation, Dalton's theory successfully explained the Laws of Conservation of Mass and Definite Proportions and remains foundational to chemistry.

Test: Atomic Foundations of Matter - 2 - Question 13
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What is the correct chemical formula for calcium carbonate?

Detailed Solution: Question 13

Calcium ion (Ca²⁺) has charge 2+ and carbonate ion (CO₃²⁻) has charge 2−. Using the criss-cross method, subscript of Ca = 2 and subscript of CO₃ = 2, initially giving Ca₂(CO₃)₂. Since both subscripts are equal, we simplify by dividing both by 2, giving the final formula CaCO₃. The formula always represents the simplest whole number ratio of ions.

Test: Atomic Foundations of Matter - 2 - Question 14
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A student placed 4.0 g of calcium carbonate and 2.92 g of hydrochloric acid in a closed container. After the reaction, 1.76 g of CO₂, 0.72 g of water, and 4.44 g of calcium chloride were formed. Which law does this verify?

Detailed Solution: Question 14

Total mass of reactants = 4.0 + 2.92 = 6.92 g. Total mass of products = 1.76 + 0.72 + 4.44 = 6.92 g. Since mass of reactants = mass of products (6.92 g = 6.92 g), this experiment directly verifies the Law of Conservation of Mass, which states that matter can neither be created nor destroyed in a chemical reaction. The closed container ensures no gas escapes, keeping the system perfectly closed.

Test: Atomic Foundations of Matter - 2 - Question 15
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Which of the following molecules contains a double covalent bond?

Detailed Solution: Question 15

Oxygen has 6 electrons in its valence shell and needs 2 more electrons to complete its octet. Two oxygen atoms each share 2 electrons with each other, forming a shared pair of 2 electrons on each side. This results in a double covalent bond represented as O=O. In contrast, H₂ and Cl₂ have single covalent bonds (each atom shares only 1 electron), and HCl also has a single covalent bond between hydrogen and chlorine.

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This test contains 15 MCQs on Atomic Foundations of Matter - 2 with detailed solutions for each question. It is part of the Science Class 9 New NCERT 2026-27 (New Syllabus) course on EduRev, designed to align with the current Class 9 syllabus. Each solution explains not just the correct answer but also gives you an understanding of the topic — not just to attempt the question but also help you prepare for the exam with practice.

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