CBSE Class 8 Science Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures — Assertion & Reason
CBSE Class 8 Science Assertion & Reason
Expert crafted · Instant PDF download · 2026-27
The following Assertion and Reason questions are based on Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures from the NCERT Class 8 Science textbook Curiosity. Each question has four options — read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(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 R is true.
(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 R is true.
Assertion & Reason Questions
1
Assertion (A): A mixture is formed when two or more substances are mixed together.
Reason (R): In a mixture, the components retain their individual properties and do not react chemically with each other.
Reason (R): In a mixture, the components retain their individual properties and do not react chemically with each other.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The definition of a mixture is precisely that the substances maintain their own properties without undergoing chemical change.
2
Assertion (A): Air is a uniform mixture.
Reason (R): The different components of air like nitrogen, oxygen, and carbon dioxide are evenly distributed and cannot be distinguished even with a microscope.
Reason (R): The different components of air like nitrogen, oxygen, and carbon dioxide are evenly distributed and cannot be distinguished even with a microscope.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Air is uniform because its gaseous components are evenly mixed throughout and cannot be seen separately.
3
Assertion (A): Sugar dissolved in water is a uniform mixture.
Reason (R): Sugar particles occupy the interparticle spaces present between water particles.
Reason (R): Sugar particles occupy the interparticle spaces present between water particles.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While sugar solution is uniform and sugar does occupy spaces between water particles, R explains why volume decreases, not why the mixture is uniform.
4
Assertion (A): Alloys like brass and bronze are uniform mixtures.
Reason (R): In alloys, metals are mixed so uniformly that individual substances cannot be seen throughout the mixture.
Reason (R): In alloys, metals are mixed so uniformly that individual substances cannot be seen throughout the mixture.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Alloys are uniform mixtures where metals are so thoroughly mixed that the entire mixture appears the same throughout.
5
Assertion (A): In science, pure milk is not considered a pure substance.
Reason (R): A pure substance in science is one that consists of the same type of particles and cannot be separated into other kinds of matter by physical processes.
Reason (R): A pure substance in science is one that consists of the same type of particles and cannot be separated into other kinds of matter by physical processes.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Milk contains multiple substances (water, fats, proteins, sugars), so it's a mixture, not a pure substance despite being called 'pure milk' commercially.
6
Assertion (A): When electricity is passed through water, it breaks down into hydrogen and oxygen.
Reason (R): Water is a compound made of two different elements chemically combined in a fixed ratio.
Reason (R): Water is a compound made of two different elements chemically combined in a fixed ratio.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Water can be broken down by electricity into its constituent elements because it is a compound formed from hydrogen and oxygen in a 2:1 ratio.
7
Assertion (A): Elements are the building blocks of all matter.
Reason (R): Elements can be broken down into simpler substances by chemical reactions.
Reason (R): Elements can be broken down into simpler substances by chemical reactions.
Answer: (c)
A is true, but R is false. Elements are indeed the building blocks of matter, but they CANNOT be broken down into simpler substances by any chemical means—that's what defines them as elements.
8
Assertion (A): Hydrogen and oxygen atoms cannot exist independently.
Reason (R): Two atoms of hydrogen combine to form one molecule of hydrogen, and two atoms of oxygen combine to form one molecule of oxygen.
Reason (R): Two atoms of hydrogen combine to form one molecule of hydrogen, and two atoms of oxygen combine to form one molecule of oxygen.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. These atoms must combine with each other to form stable molecules because they cannot exist independently in nature.
9
Assertion (A): Water is a compound.
Reason (R): Hydrogen and oxygen in water cannot be separated by physical methods.
Reason (R): Hydrogen and oxygen in water cannot be separated by physical methods.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Water is a compound because its constituent elements are chemically combined and cannot be separated by physical means—only by chemical processes like electrolysis.
10
Assertion (A): Sugar is a compound consisting of carbon, hydrogen, and oxygen.
Reason (R): When sugar is heated, it decomposes to give carbon (charcoal) and water.
Reason (R): When sugar is heated, it decomposes to give carbon (charcoal) and water.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The decomposition of sugar into carbon and water (which itself contains hydrogen and oxygen) proves it is a compound made of these three elements.
11
Assertion (A): The properties of compounds are different from those of their constituent elements.
Reason (R): Hydrogen is a fuel, oxygen supports combustion, but water (formed from both) extinguishes fire.
Reason (R): Hydrogen is a fuel, oxygen supports combustion, but water (formed from both) extinguishes fire.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. This example perfectly demonstrates how compounds have entirely different properties from their constituent elements.
12
Assertion (A): A mixture of iron filings and sulfur powder can be separated using a magnet.
Reason (R): Iron filings are attracted to a magnet, while sulfur is not.
Reason (R): Iron filings are attracted to a magnet, while sulfur is not.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Since components in a mixture retain their individual properties, iron maintains its magnetic property and can be separated from non-magnetic sulfur.
13
Assertion (A): When a mixture of iron and sulfur is heated, it forms iron sulfide which is not attracted to a magnet.
Reason (R): Iron sulfide is a compound with properties completely different from both iron and sulfur.
Reason (R): Iron sulfide is a compound with properties completely different from both iron and sulfur.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Chemical combination during heating forms a new compound with new properties, losing the magnetic property of iron.
14
Assertion (A): Most minerals are compounds rather than pure elements.
Reason (R): Native minerals like gold, silver, and copper are pure elements found in nature.
Reason (R): Native minerals like gold, silver, and copper are pure elements found in nature.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While most minerals are compounds, some (native minerals) are pure elements—R provides an exception rather than explaining A.
15
Assertion (A): Lime water turns milky when exposed to air for some time.
Reason (R): Carbon dioxide present in air reacts with calcium hydroxide (lime water) to form calcium carbonate.
Reason (R): Carbon dioxide present in air reacts with calcium hydroxide (lime water) to form calcium carbonate.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The milky appearance is due to formation of insoluble calcium carbonate when CO₂ from air reacts with lime water, demonstrating the presence of carbon dioxide in air.
❓ Frequently Asked Questions
What is covered in CBSE Class 8 Science Chapter 8 Nature of Matter: Elements, Compounds, and Mixtures?
This chapter covers all key topics from Nature of Matter: Elements, Compounds, and Mixtures as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 8 board exam preparation covering the complete syllabus.
Are these CBSE Class 8 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 8 Science?
All chapters of CBSE Class 8 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
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