Q11: Explain the difference between 2H and H2.

A11: The notation 2H represents two free hydrogen atoms. The notation H2 represents one molecule of H2

Atoms and Molecules Class 9 Case Study Questions Science Chapter 3

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Last Updated on April 15, 2025 by XAM CONTENT

Hello students, we are providing case study questions for class 9 science. Case study questions are the new question format that is introduced in CBSE board. The resources for case study questions are very less. So, to help students we have created chapterwise case study questions for class 9 science. In this article, you will find case study questions for cbse class 9 science chapter 3 Atoms and Molecules.

Chapter	Atoms and Molecules
Type of Questions	Case Study Questions
Nature of Questions	Competency Based Questions
Board	CBSE
Class	9
Subject	Science
Theme	Moving Things, People and Ideas
Useful for	Class 9 Studying Students
Answers provided	Yes
Difficulty level	Mentioned
Important Link	Class 9 Science Chapterwise Case Study

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Table of Contents

Case Study Questions on Atoms and Molecules

Questions

Question 1:

The chemical formula of a compound represents the types and number of atoms present. To write a chemical formula, we use the symbols of elements and their valency. For example, in calcium chloride (CaCl₂), calcium has a valency of 2 and chlorine has a valency of 1, hence two Cl⁻ ions are needed to balance one Ca²⁺ ion. Understanding this helps in naming and balancing chemical equations properly.

Q1. What is the valency of calcium in CaCl₂?
(a) 1
(b) 2
(c) 3
(d) 0

Q2. In the formula CaCl₂, how many chlorine atoms are present?
(a) 1
(b) 2
(c) 3
(d) 0

Q3. The total number of atoms in one molecule of H₂SO₄ is:
(a) 5
(b) 6
(c) 7
(d) 4

Q4. Which of the following is correctly matched with its chemical formula?
(a) Magnesium Oxide – MgO
(b) Sodium Chloride – Na₂Cl
(c) Aluminium Oxide – AlO
(d) Potassium Sulphate – KSO₄

Answers:
Q1. (b)
Q2. (b)
Q3. (c)
Q4. (a)

Question 2:

Antoine Lavoisier laid the foundation for the modern concept of chemical reactions through the Law of Conservation of Mass, which states that mass can neither be created nor destroyed. Later, Joseph Proust proposed the Law of Constant Proportions, which stated that a given compound always contains the same elements in the same proportion by mass. These laws helped in developing Dalton’s Atomic Theory, which revolutionized how we understand chemical combinations. For example, in water (H₂O), the mass ratio of hydrogen to oxygen is always 1:8, no matter the source.

Q1. Which law states that mass remains unchanged in a chemical reaction?
(a) Law of Constant Proportions
(b) Law of Conservation of Mass
(c) Law of Multiple Proportions
(d) Law of Definite Volume

Q2. In water (H₂O), the ratio of hydrogen to oxygen by mass is:
(a) 2:16
(b) 1:2
(c) 1:8
(d) 8:1

Q3. The Law of Constant Proportion was given by:
(a) Dalton
(b) Avogadro
(c) Lavoisier
(d) Proust

Q4. Dalton’s Atomic Theory helped in:
(a) Discovery of oxygen
(b) Proving the wave nature of light
(c) Explaining chemical combination
(d) Explaining gravity

Answers:
Q1. (b)
Q2. (c)
Q3. (d)
Q4. (c)

Also check

Case study questions for other chapters of class 9 science is given below.

We hope the given case study questions for Atoms and Molecules Class 9 helps you in your learning.

Helpful Links for CBSE Class 9 Science Preparation

Topics from which case study questions may be asked

Laws of Chemical Combination
Dalton’s Atomic Theory
Writing Chemical Formulae Using Valency
Mole Concept and Avogadro’s Number
Numerical Conversions: Mole, Mass, and Number of Particles

Maharishi Kanad, an Indian Philosopher proposed that matter is made up of small particles called parmanu. The Greek Philosopher, Democritus proposed that matter is made up of extremely small particles called atoms.

The smallest atom (by mass) in the periodic table is the hydrogen atom with one proton and one electron while the atom with smallest atomic radius is the helium atom (atomic radius = 31pm).

For further practice on case study questions related to Atoms and Molecules Class 9 Science, we recommend exploring the link given below.

Practice More Case Study Questions on “Atoms and Molecules”

Frequently Asked Questions (FAQs) on Atoms and Molecules Case Study Questions

Q1: What are case study questions for CBSE examinations?

A1: Case study questions in CBSE examinations typically involve scenarios or real-life examples, requiring students to apply their understanding of concepts to solve problems or analyze situations.

Q2: Why are case study questions important for understanding class 9 science chapters?

A2: Case study questions provide a practical context for students to apply theoretical knowledge to real-world situations, fostering deeper understanding and critical thinking skills.

Q3: How should students approach answering case study questions for CBSE?

A3: Students should carefully read the case study, identify the key issues or problems presented, analyze the information provided, apply relevant concepts and principles of chemical reactions and equations, and formulate well-supported solutions or responses.

Q4: Are there any resources available online for students to practice case study questions on class 9 science chapters for CBSE exams?

A4: Yes, several educational websites offer case study questions for CBSE students preparing for science examinations. We also offer a collection of case study questions for all classes and subject on our website. Visit our website to access these questions and enhance your learning experience. If you need more case study questions for your preparation, then you visit Physics Gurukul website.

Q5: How can students effectively prepare for case study questions on “Atoms and Molecules” for CBSE exams?

A5: Effective preparation strategies include regular revision of concepts, solving practice questions, analyzing case studies from previous exams, seeking clarification on doubts, and consulting with teachers or peers for guidance and support.

Q6: How can teachers incorporate case study questions on “Atoms and Molecules” class 9 science into classroom teaching?

A6: Teachers can integrate case studies into lesson plans, group discussions, or interactive activities to engage students in active learning, promote problem-solving skills, and facilitate a deeper understanding of “Atoms and Molecules”.

Q7: Who proposed the law of constant proportions?

A7: Antoine L. Lavoisier

Q8: State law of conservation of mass.

A8: Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.

Q9: Why is it not possible to see an atom with naked eyes?

A9: It is not possible to see an atom with naked eyes because it is very small in size. Atomic radius is measured in nanometer, 1 nm = 10^–9 m.

Q10: Define atomicity.

A10: The total number of all types of atoms in one molecule of a substance is called its atomicity.
For example, atomicity of hydrogen in H₂ is two, atomicity of oxygen in ozone O₃ is three.

Q11: Explain the difference between 2H and H₂.

A11: The notation 2H represents two free hydrogen atoms. The notation H₂ represents one molecule of H₂

Q12: Define molecule.

A12: A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. A molecule in general a group of two or more atoms join together in small groups.

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