Class 8 Science Chapter 8 NCERT Solutions: Nature of Matter, Elements, Compounds, and Mixtures

1. Multiple choice questions.

1. Consider the following reaction where two substances, A and B, combine to form a product C:
A + B → C
Assume A and B cannot be broken down into simpler substances chemically. Which is correct?

• (a) A, B, and C are all compounds and only C has a fixed composition.
• (b) C is a compound, and A and B have a fixed composition.
• (c) A and B are compounds, and C has a fixed composition.
• (d) A and B are elements, C is a compound, and has a fixed composition.

Answer: (d) A and B are elements, C is a compound, and has a fixed composition.

2. Assertion: Air is a mixture.
Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

• (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
• (b) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
• (c) Assertion is true, but Reason is false.
• (d) Assertion is false, but Reason is true.

Answer: (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

2. Answer the following questions in about 30 words.

1. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Answer: Water is a compound formed by chemical combination of hydrogen and oxygen in a fixed ratio. Its properties differ completely from its constituent elements; hydrogen and oxygen are gases whereas water is a liquid. Water neither supports combustion like oxygen nor is flammable like hydrogen.

2. In which of the following cases are all the examples correctly matched? Give reasons.

• (a) Elements — water, nitrogen, iron, air.
• (b) Uniform mixtures— minerals, seawater, bronze, air.
• (c) Pure substances— carbon dioxide, iron, oxygen, sugar.
• (d) Non-uniform mixtures — air, sand, brass, muddy water.

Answer: (c) Pure substances—carbon dioxide, iron, oxygen, sugar. Only option (c) correctly lists pure substances. Carbon dioxide (compound), iron and oxygen (elements), and sugar (compound) are all pure substances because they consist of only one kind of particle.

3. Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances as elements, compounds, or mixtures, with justification.

Answer: Iron and magnesium are elements. Air is a mixture. Iron oxide and magnesium oxide are compounds because they are formed by chemical combination of elements. Oxygen is an element. Classification: Iron—element, moist air—mixture, iron oxide—compound; magnesium—element, oxygen—element, magnesium oxide—compound.

4. Classify the following as elements, compounds, or mixtures in Table 8.3.
Carbon dioxide, sand, seawater, magnesium oxide, muddy water, aluminium, gold, oxygen, rust, iron sulfide, glucose, air, water, fruit juice, nitrogen, sodium chloride, sulfur, hydrogen, baking soda.

Pure substances: Aluminium, Gold, Oxygen, Nitrogen, Sulfur, Hydrogen, Carbon dioxide, Magnesium oxide, Rust, Iron sulfide, Glucose, Water, Sodium chloride, Baking soda.

5. What new substance is formed when a mixture of iron filings and sulfur powder is heated, and how is it different from the original mixture? Also, write the word equation for the reaction.

Answer: On heating, iron filings and sulfur powder react to form iron sulfide, a compound. It is uniform, properties differ from the original elements, and cannot be separated by physical methods. Word equation: Iron + Sulfur → Iron sulfide.

6. Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.

Answer: No, a substance cannot be classified as both an element and a compound. An element consists of only one type of atom and cannot be broken down further, while a compound is formed by the chemical combination of two or more elements in a fixed ratio.

7. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Answer: If water were just a mixture of hydrogen and oxygen, its properties would not be the same. It would not serve as a solvent for life activities and could be explosive, making it unsafe and unsuitable for drinking, cleaning, or supporting life.

8. Analyse Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Answer: Gas A is hydrogen. The word equation of the reaction is:
Water → Hydrogen + Oxygen (on passing electricity through water).

9. Write the names of any two compounds made only from non-metals, and mention two uses of each.

Answer: Carbon dioxide—used in fire extinguishers, carbonated drinks. Sulfur dioxide—used as a preservative and in bleaching. Both are compounds formed from only non-metals.

10. How can gold be classified as both a mineral and a metal?

Answer: Gold is considered a mineral when found in its native (elemental) form in the earth. It is also a metal because of its metallic properties such as luster, malleability, and conductivity.

Understanding Elements, Compounds, and Mixtures – Class 8 Science NCERT Solutions 2025-26

Master the basics of matter—elements, compounds, and mixtures—with structured NCERT Class 8 Science Chapter 8 solutions for 2025-26. Knowing how substances combine and separate is fundamental for acing your exams.

Practice concept-driven questions and real-life examples to clarify distinctions between pure substances and mixtures. Regular revision of these NCERT exercise questions will sharpen your understanding and boost your confidence in Science.

Stay ahead with chapter-wise NCERT solutions and exam tips for elements, compounds, and mixtures. Focus on key definitions, practice the short and long answer questions, and review tables for quick learning and strong exam preparation.