NCERT Solutions for Class 9 Science Chapter 9 Atomic Foundations of Matter provide clear, step-by-step answers to every exercise and in-text question from the chapter Atomic Foundations of Matter of the NCERT textbook Exploration. Prepared by subject experts as per the latest NCERT (CBSE) syllabus for 2026-27, these NCERT Solutions for Class 9 Science help you understand each concept, write exam-ready answers, and check your own solutions. You can read them online below or download the free Class 9 Science Chapter 9 question-answer PDF.
NCERT Solutions for Class 9 Science Chapter 9 Atomic Foundations of Matter
- Class: Class 9
- Subject: Science
- Chapter: Chapter 9 – Atomic Foundations of Matter
- Textbook: Exploration (NCERT)
- Study material: NCERT Solutions – questions with answers, free PDF
These solutions answer all the exercise questions of Chapter 9 Atomic Foundations of Matter — including the in-text questions, short-answer and long-answer questions, and activities — with complete explanations so you can follow the method, not just the final answer. Read the full solutions below.
NCERT Solutions Class 9 Science Chapter 9 Atomic Foundations of Matter View Download
NCERT Solutions for Class 9 Science Chapter 9 PDF Download
You can read the NCERT Solutions for Class 9 Science Chapter 9 online above, or download the complete question-answer PDF to study Atomic Foundations of Matter offline at any time.
NCERT Solutions for Class 9 Science Chapter 9 PDF Download Link – Click Here to Download Solutions PDF
Questions Covered in This Chapter
These NCERT Solutions answer all 63 questions of this chapter. The questions solved are:
- Water can be obtained from various sources. Are all these samples of water chemically identical?
- Oxygen is sometimes represented as O and sometimes as O2. What is the difference between these symbols?
- Why does dissolved salt in water conduct electricity, but sugar does not?
- What do you observe? (after swirling until the added salt dissolves)
- (Experimental set-up 1, step 8) What do you observe?
- (Experimental set-up 1, step 9) Are the initial and the final readings same?
- A brisk effervescence is observed. The final reading does not match the initial reading. What can be the reason for this?
- (Experimental set-up 2, step 8) What do you observe?
- (Experimental set-up 2, step 11) Are the initial and the final readings same in this case?
- (Step 7) What do you observe?
- (Step 9) Do you observe any change in the reading after mixing the solutions?
- You are given a chemical reaction in which zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas. Zinc + Hydrochloric acid (dilute) → Zinc chloride + Hydrogen. Design and perform an experiment to test the hypothesis that mass is conserved during the chemical reaction. You may use a set-up different from the one shown in Activity 9.2.
- A student burns 10 g of ethanol in an open beaker. After the reaction, no residue is left in the beaker. Does this mean the Law of Conservation of Mass is violated? Explain.
- When 20 g of hydrogen reacts completely with 160 g of oxygen, how much water is formed according to the Law of Conservation of Mass?
- A compound consists of 40% sulfur and 60% oxygen by mass. In a sample of the same compound containing 20 g of sulfur, what mass of oxygen must be present to satisfy the Law of Constant Proportions?
- Carbon monoxide (CO) contains carbon and oxygen in the mass ratio of 3:4. How much oxygen will combine with 9 g of carbon to form carbon monoxide?
- The Law of Definite Proportions holds true for compounds but not for mixtures. Give reason.
- Students X and Y, both prepared an oxide of copper by combining copper and oxygen in the ratios of 4:1 and 8:2, respectively. Do their results justify the Law of Constant Proportions? Explain.
- What if … atoms could combine in any ratio and not in a fixed ratio? How would this affect the substances around us?
- Assertion (A): 2 g of hydrogen combines with 16 g of oxygen to form 18 g of water. Reason (R): According to Dalton’s Atomic Theory, atoms combine in a simple whole number ratio by mass to form compounds. Choose the correct option: (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true.
- Nitrogen has five valence electrons. Draw the structure of the nitrogen molecule (N2).
- The atomic number of fluorine is 9. Explain the formation of the fluorine molecule (F2).
- Show the formation of the following molecules: (i) Carbon dioxide (CO2) (ii) Hydrogen sulfide (H2S) (iii) Ammonia (NH3)
- Neon (atomic number 10) neither transfers nor shares its valence electrons. Explain.
- If the valence shell of an atom has less than four electrons, it would generally donate its valence electrons to achieve a stable electronic configuration. Identify four such elements among the first 18 elements by using their electronic configurations given in Table 8.4 of the Chapter 8, Journey Inside the Atom.
- Will it still be neutral after losing one electron? If not, what charge would it carry and why?
- What if … we could see atoms directly? How would it help scientists and what challenges would it cause?
- What kind of ion will oxygen (O) form?
- Fill in the blanks. Among magnesium and chlorine, magnesium atom can give two electrons to become Mg2+. However, chlorine can take only one electron to become ____________. Now, __________ ion of magnesium and __________ ions of chlorine combine to give magnesium chloride.
- Show the formation of cations of potassium (K) and calcium (Ca) atoms, and the formation of their corresponding chlorides using diagrams.
- Illustrate how sodium sulfide (Na2S) is formed.
- Name the following: (i) CO2 (ii) NO2 (iii) SF6 (iv) PCl3
- Write the formula for the following: (i) Sodium hydrogencarbonate (ii) Sulfur dioxide (iii) Ferric chloride (iv) Cuprous oxide
- Write the formulae for the compounds formed from the following pairs of ions: (i) Fe3+ and OH‒ (ii) K+ and CO3 2–
- (Step 9) Group the compounds showing similar properties listed in Table 9.2.
- Other covalent compounds, such as camphor and naphthalene, also do not conduct electricity. Can you give a reason?
- Predict whether ionic and covalent compounds would conduct electricity in the molten state (the melted state of a substance).
- What type of chemical bond is present in a solid compound that does not conduct electricity in the solid state but conducts electricity when dissolved in water?
- Metal M, with two electrons in its valence shell (M shell), reacts with oxygen to form a compound that is slightly soluble in water. Predict its: (i) formula (ii) type of bond (iii) electrical conductivity of its aqueous solution.
- Find the molecular mass of nitric acid (HNO3). Atomic mass — H = 1 u; N = 14 u; O = 16 u.
- Find the molecular mass of methane (CH4). Atomic mass — C = 12 u; H = 1 u.
- Find the formula unit mass of potassium chloride (KCl). Atomic mass — K = 39 u; Cl = 35.5 u.
- Find the formula unit mass of magnesium hydroxide, Mg(OH)2. Atomic mass — Mg = 24 u; O = 16 u; H = 1 u.
- A particular element (A) has one electron in its third shell. There is another element (B) with six electrons in its second shell. (i) How many electrons does A tend to give or take to become stable? (ii) What kind of ion would it form? (iii) How many electrons does B tend to give or take to become stable? (iv) What kind of ion would it form? (v) If A and B were to combine, what kind of bond would be formed? (vi) What would be the formula for the compound thus formed?
- An element X has six electrons in its outer shell and forms a diatomic molecule. (i) Why would that be so? (ii) What kind of bond would it form? (iii) Draw the structure of the molecule it would form. (iv) A certain other element Y has two electrons in its second shell. Draw the structure of the molecule that X would form with Y.
- You want to design a new ionic compound, where the total positive charge is 6+ and the total negative charge is 6 –. Which of the following combinations gives the correct number of ions? (i) 2 Al3+ and 3 Cl– (ii) 3 Mg2+ and 1 PO4 3– (iii) 2 Fe3+ and 3 O2– (iv) 3 Ca2+ and 2 SO4 2–
- Choose the correct statement(s) and correct the false statement(s). (i) Elements are made up of molecules and compounds are made up of atoms. (ii) The molecule of a compound is always made up of two or more atoms of the same kind. (iii) One molecule of nitrogen gas contains three nitrogen atoms. (iv) Water is made of two hydrogen atoms, covalently bonded with one oxygen atom.
- Write the chemical formulae for the following compounds. (i) Aluminium nitrate (ii) Calcium oxide (iii) Ferric oxide
- Write the formulae of the compounds formed from the following pairs of ions. (i) Ca2+ and Br‒ (ii) Al3+ and CO3 2– (iii) K+ and SO4 2– (iv) NH4 + and Cl–
- Which of the following, in Fig. 9.18, correctly represents Cl– ion (Atomic number of chlorine = 17).
- Determine the formula unit mass of the following substances. (i) Ammonium nitrate (NH4NO3), used as a nitrogen fertiliser, which is essential for plant growth. (ii) Phosphoric acid (H3PO4), used to make phosphate fertiliser and detergents. (iii) Sodium hydrogencarbonate (NaHCO3), used to relieve acidity and helps in digestion.
- Write the formulae for the compounds formed by the reaction of: (i) Magnesium and nitrogen (ii) Lithium and nitrogen (iii) Sodium and sulfur (iv) Aluminium and oxygen
- Complete the Table 9.3 by writing the formulae of the compounds formed by the cations on the left and the anions at the top. LiNO3 is given as an example.
- 5.3 g of sodium carbonate and 6.0 g of acetic acid react to produce 2.2 g of carbon dioxide, 0.9 g of water, and 8.2 g of sodium acetate. Verify whether the law of conservation of mass is valid.
- If a species has 11 protons, 12 neutrons and 10 electrons then (i) what is its atomic number and mass number? (ii) is it neutral, a cation or an anion? Explain. (iii) write its electronic configuration. (iv) name the species.
- Two elements, A and B, have the following configurations — A: 2, 8, 5 B: 2, 8, 7 (i) Which element is more reactive? (ii) Will A and B form ionic or covalent bonds when they combine? Explain using electron transfer or sharing. (iii) Predict the formula of the compound they would form.
- Assertion (A): Copper sulfate conducts electricity in the molten state but not in the solid state. Reason (R): Copper and sulfate ions are fixed in the lattice in molten state, while in solid state they can move freely. Choose the correct option: (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true.
- The species 27Al, 80Br– and 201Hg2+ have 13, 35 and 80 protons, respectively. How many electrons and neutrons do they have?
- Design and perform an experiment to show and compare that water always contains hydrogen and oxygen in the same ratio, regardless of its source.
- Compare atoms and ions of any three elements. Show the number of electrons before and after ion formation using bar graphs.
- Make a card game with cations and anions. Possible ideas may include — Pick cards from the pile or from open cards and match them with cards in your hand to form compounds. You may discard any unwanted cards. Ask other players for cards and form compounds using the cards they already have.
- To learn more about molecules you can explore the link given below —
- Are there any chemical changes that do not obey the Law of Conservation of Mass?
Chapter at a Glance
- Law of Conservation of Mass (Lavoisier, 1789): in a chemical reaction matter is neither created nor destroyed, so the total mass of the reactants equals the total mass of the products. It only looks violated in an open vessel, because a gaseous product walks off the balance pan.
- Law of Constant Proportions (Proust): a compound always contains the same elements in the same fixed ratio by mass, whatever its source. Pure water from a river, a borewell or the ocean is always H : O = 1 : 8 by mass.
- Dalton's atomic theory explains both laws with one picture — atoms are indivisible in a chemical reaction and merely rearrange, atoms of one element are identical in mass, and atoms combine in simple whole-number ratios.
- Atoms combine to reach a stable octet (a duplet for the K-shell). They do it in two ways: by sharing electrons — a covalent bond (H—H, O=O, N≡N, H—Cl) — or by transferring them, giving a cation and an anion held by electrostatic attraction — an ionic bond (Na⁺Cl⁻).
- Ionic solids are 3-D crystal lattices, not molecules; they are usually soluble in water, insoluble in kerosene and petrol, have high melting points, and conduct only when their ions are free to move (dissolved or molten). Covalent compounds are the reverse on nearly every count.
- A chemical formula is written by criss-crossing valencies or charges and then dividing by any common factor: Ca²⁺ + Cl⁻ → CaCl₂; Al³⁺ + O²⁻ → Al₂O₃; Mg²⁺ + OH⁻ → Mg(OH)₂.
- Molecular mass (covalent compounds) and formula unit mass (ionic compounds) are both got by adding up the atomic masses of every atom in the formula: H₂O = 18 u, CO₂ = 44 u, Na₂O = 62 u, Ca(NO₃)₂ = 164 u.
How to Download NCERT Solutions for Class 9 Science Chapter 9 PDF
Follow these simple steps to get the Atomic Foundations of Matter questions-and-answers PDF from Exploration.
- Search NCERT Solutions for Class 9 Science Chapter 9 aglasem and open this page.
- Read the exercise questions with answers for Atomic Foundations of Matter shown above.
- Click the Download PDF link to save the Atomic Foundations of Matter solutions to your device.
NCERT Solutions for Class 9 Science – All Chapters
There are more chapters to study besides Atomic Foundations of Matter in Science. Here are the NCERT Solutions for all chapters of Class 9 Science.
- Chapter 1 Exploration Entering the World of Secondary Science
- Chapter 2 Cell the Building Block of Life
- Chapter 3 Tissues in Action
- Chapter 4 Describing Motion Around Us
- Chapter 5 Exploring Mixtures and Their Separation
- Chapter 6 How Forces Affect Motion
- Chapter 7 Work Energy and Simple Machines
- Chapter 8 Journey Inside the Atom
- Chapter 9 Atomic Foundations of Matter
- Chapter 10 Sound Waves Characteristics and Applications
- Chapter 11 Reproduction How Life Continues
- Chapter 12 Patterns in Life Diversity and Classification
- Chapter 13 Earth As a System Energy Matter and Life
NCERT Solutions for Class 9 – All Subjects
Just like Chapter 9 of Science, you can get the exercise questions with answers for every other subject of Class 9. Here are the NCERT Solutions for all subjects of Class 9.
NCERT Solutions for Class 9 Science Chapter 9 – An Overview
The key highlights of this study material are as follows.
| Aspects | Details |
|---|---|
| Class | Class 9 |
| Subject | Science |
| Chapter Number | Chapter 9 |
| Chapter Name | Atomic Foundations of Matter |
| Book Name | Exploration |
| Book By | NCERT (National Council of Educational Research and Training) |
| Educational Resource Here | NCERT Solutions of Class 9 Science Chapter 9 for all exercises |
| More Questions Answers of This Subject | NCERT Solutions for Class 9 Science |
| Download Book Chapter | NCERT Book Class 9 Science |
| All Questions Answers For This Class | NCERT Solutions for Class 9 |
| Complete Solutions | NCERT Solutions |
NCERT Solutions for Class 9 Science Chapter 9 Atomic Foundations of Matter – FAQs
What are the NCERT Solutions for Class 9 Science Chapter 9 Atomic Foundations of Matter?
They are the complete, step-by-step answers to all the exercise and in-text questions of Chapter 9 Atomic Foundations of Matter from the NCERT Class 9 Science textbook Exploration, written by experts as per the latest NCERT syllabus.
How can I download the Class 9 Science Chapter 9 solutions PDF for free?
Open this page on aglasem, read the Atomic Foundations of Matter questions with answers, and click the “Download Solutions PDF” link. The Class 9 Science Chapter 9 NCERT Solutions PDF is completely free to download.
Are these NCERT Solutions as per the latest 2026-27 syllabus?
Yes. The NCERT Solutions for Class 9 Science Chapter 9 are based on the latest NCERT textbook Exploration and the current 2026-27 CBSE syllabus, so the questions and answers match what you study in class.
Where can I get NCERT Solutions for the other chapters of Class 9 Science?
You can find the answers to every chapter on the NCERT Solutions for Class 9 Science page, and solutions for every subject on the NCERT Solutions for Class 9 page.
How do NCERT Solutions help in exam preparation?
They show the correct method to solve each question, help you write answers the way they are expected in exams, let you check and correct your own work, and save revision time — which together improve your marks in Class 9 Science.
If you have any queries on NCERT Solutions for Class 9 Science Chapter 9 Atomic Foundations of Matter, then please ask in the comments below.
