Are there any numerical problems in important questions in Class 9 Science Chapter 3?

Yes, there are a few multiple-choice questions as numerical. Students should practise the numerical problems in Chapter 3 of Class 9 Science.. For better exam results, students should practise all the numerical problems in Chapter 3 of 9 Science. They can also practise numerical questions from the NCERT books.

The most crucial element in the fundamental unit of matter is the atom. It is everywhere. Atoms are the most fundamental structure and cannot be broken, and they are also a part of our body. To understand the concept of atoms, students should carefully read NCERT Chapter 3. To learn more about atoms, they can refer to Extramarks' Important Questions for CBSE Class9 Science Atoms and Molecules.

Which are the essential topics covered in the list of important questions in Class 9 Science Chapter 3?

Students will study the definitions of atoms and molecules in Class 9 Science Chapter 3. Students will also learn about different theories about the discovery of atoms and formation. In addition, students will learn how to create a chemical formula for any compound. Further, they will understand the laws of constant proportion and other laws relating to chemical reactions. Chapter 3 of Class 9 Science also includes essential topics such as molecule mass and mole.

CBSE Important Questions Class 9 Science Chapter 3 – Atoms and Molecules

Class 9 Science Chapter 3 Atoms and Molecules is part of the CBSE Class 9 Science syllabus. It explains the laws of chemical combination, the idea of atoms and molecules, how to write chemical symbols and formulae, valency, ions and polyatomic ions. Students also learn about atomic mass, molecular mass, the mole concept and how to use it to work out the number of particles and the mass of a substance.

These CBSE important questions for Class 9 Science Chapter 3 cover ionic compounds, naming compounds from their formulae, the meaning of chemical symbols such as 2H and N2, the formula of aluminium hydroxide, molar volume at STP, vapour density, the number of neutrons, mass percentage, the mole concept and the laws of conservation of mass and constant proportions. Every question has a clear step-by-step answer in simple English, so students can practise on their own, parents can check the working, and teachers can use them for class tests.

Q1. An ionic compound is made up of
(a) metal and non-metal
(b) cation and cation
(c) anion and anion
(d) metal and metal

Answer: (a) metal and non-metal
A metal loses electrons and becomes a positive ion (cation), while a non-metal gains those electrons and becomes a negative ion (anion). The strong attraction between these opposite charges forms the ionic bond, as in sodium chloride (NaCl).

Q2. Write the names of the following compounds:
(a) Ca₃(PO₄)₂
(b) NaHCO₃
(c) (NH₄)₂SO₄
(d) MgCO₃
(e) FeSO₄
(f) AlCl₃

Answer: (a) Calcium phosphate
(b) Sodium hydrogen carbonate (sodium bicarbonate)
(c) Ammonium sulphate
(d) Magnesium carbonate
(e) Ferrous sulphate (iron(II) sulphate)
(f) Aluminium chloride

Q3. Write the meaning of the following abbreviations.
(a) C
(b) 2H
(c) N₂
(d) 3N₂
(e) O₃
(f) O²⁻

Answer: (a) One atom of carbon
(b) Two atoms of hydrogen
(c) One molecule of nitrogen
(d) Three molecules of nitrogen
(e) One molecule of ozone
(f) One oxide ion (an oxygen atom that has gained two electrons)

Q4. The formula of aluminium hydroxide is
(a) Al(OH)₃
(b) Al₂(OH)₃
(c) Al(OH)₂
(d) Al₄(OH)₃

Answer: (a) Al(OH)₃
The aluminium ion has a charge of +3 and the hydroxide ion has a charge of −1. To make the compound neutral, three hydroxide ions are needed for one aluminium ion, giving Al(OH)₃.

Q5. What volume, at STP, is occupied by 4 moles of ammonia gas?
(a) 24.09 L
(b) 84.4 L
(c) 89.6 L
(d) 86.8 L

Answer: (c) 89.6 L
At STP, 1 mole of any gas occupies 22.4 L.
Volume = 4 × 22.4 = 89.6 L

Q6. The vapour density of a substance is 65. What will be the molecular mass of this substance?
(a) 22
(b) 32
(c) 195
(d) 130

Answer: (d) 130
Molecular mass = 2 × vapour density
= 2 × 65 = 130

Q7. The molecular weight of a gas is 18. The vapour density of this gas will be
(a) 9
(b) 54
(c) 6
(d) 36

Answer: (a) 9
Vapour density = molecular mass ÷ 2
= 18 ÷ 2 = 9

Q8. An atom has a mass number 206 and atomic number 91. The number of neutrons present in it is
(a) 115
(b) 297
(c) 321
(d) 436

Answer: (a) 115
Number of neutrons = Mass number − Atomic number
= 206 − 91 = 115

Q9. The mass percentage of the solution obtained by dissolving 7.0 g of NaCl in 79.0 g of water is
(a) 12.21
(b) 8.86
(c) 8.14
(d) 13.29

Answer: (c) 8.14
Mass of solution = mass of solute + mass of solvent = 7.0 + 79.0 = 86.0 g
Mass percentage = (mass of solute ÷ mass of solution) × 100
= (7.0 ÷ 86.0) × 100 = 8.14%

Q10. Calculate the number of moles in 19 g of a substance whose molecular mass is 40 g.
(a) 2.11
(b) 0.96
(c) 0.48
(d) 4.21

Answer: (c) 0.48
Number of moles, n = given mass ÷ molecular mass
= 19 ÷ 40 = 0.475, that is about 0.48 mol

Q11. State the law of conservation of mass and the law of constant proportions.

Answer: Law of conservation of mass: Mass can neither be created nor destroyed in a chemical reaction. The total mass of the products is always equal to the total mass of the reactants. This law was given by Antoine Lavoisier.
Law of constant proportions (definite proportions): In a pure chemical compound, the elements are always present in a fixed ratio by mass, no matter where the compound comes from or how it is prepared. For example, in water the ratio of hydrogen to oxygen is always 1 : 8 by mass. This law was given by Joseph Proust.

Q12. Calculate the molar mass of (a) water (H₂O) and (b) carbon dioxide (CO₂).
(Atomic masses: H = 1 u, C = 12 u, O = 16 u)

Answer: (a) Water, H₂O:
= (2 × 1) + (1 × 16)
= 2 + 16 = 18 g/mol
(b) Carbon dioxide, CO₂:
= (1 × 12) + (2 × 16)
= 12 + 32 = 44 g/mol

Related Study Material on Extramarks

Q.1 Assertion (A): Seeds consist of stored food.
Reason (R): Stored food is used during germination for the initial growth of an embryo.

A. Both A and R are true and R is the correct explanation of A.

B. Both A and R are true but R is not the correct explanation of A.

C. A is true but R is false.

D. A is false but the R is true.

Marks:1
Ans

Both A and R are true and R is the correct explanation of A.

Q.2 Observe the fruit in the given image. Name the group of plants to which it belongs.

A. Angiosperms

B. Gymnosperms

C. Pteridophytes

D. Bryophytes

Marks:1
Ans

Angiosperms

Q.3 Pick the odd one out and justify your choice by giving reasons.
Coelenterates, Echinoderms, Vertebrates, Molluscs

Marks:2
Ans

Vertebrates is the odd one out because they have vertebral column while the rest are invertebrates and do not possess vertebral column.

Q.4 Enlist the characteristic features of gymnosperms.

Marks:2
Ans

The following are the characteristic features of gymnosperms:

They bear naked seeds.
They are usually perennial, evergreen and woody.

CBSE Important Questions Class 9 Science Chapter 3 – Atoms and Molecules

Related Study Material on Extramarks

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