NCERT Solutions for Class 8 Science Chapter 8 Exercise Questions
These NCERT Solutions for Class 8 Science Chapter 8 Nature of Matter: Elements, Compounds, and Mixtures provide step by step answers to all the textbook questions. They are designed to help students understand the basic concepts easily. These questions are important from an exam point of view.
Keep The Curiosity Alive
Question 1. Consider the following reaction where two substances, A and B, combine to form a product C:
A+B→C
Assume that A and B cannot be broken down into simpler substances by chemical reactions. Based on this information, which of the following statements is correct?
(i) A,B, and C are all compounds and only C has a fixed composition.
(ii) C is a compound, and A and B have a fixed composition.
(iii) A and B are compounds, and C has a fixed composition.
(iv) A and B are elements, C is a compound and has a fixed composition.
Answer:
The correct answer is option (iv).
A and B cannot be broken into simpler substances; this means they are elements. C is a compound because it is made by chemically combining two elements (A and B) in a fixed ratio.
Question 2. Assertion: Air is a mixture.
Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.
(i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
(iii) Assertion is true, but Reason is false.
(iv) Assertion is false, but Reason is true.
Answer:
The correct answer is option (i).
Air is a mixture because it consists of gases like nitrogen, oxygen, and carbon dioxide mixed together. These gases do not undergo a chemical reaction so the reason explains the assertion correctly.
Question 3. 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 the chemical combination of hydrogen and oxygen. Even though hydrogen and oxygen are gases, water is a liquid with different properties such as boiling point, taste and color. These new properties result from the chemical bond formed between the elements which shows that a compound behaves differently from its elements.
Question 4. In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.
(i) Elements - water, nitrogen, iron, air.
(ii) Uniform mixtures - minerals, seawater, bronze, air.
(iii) Pure substances - carbon dioxide, iron, oxygen, sugar.
(iv) Non-uniform mixtures - air, sand, brass, muddy water.
Answer:
The correct answer is option (iii).
The pure substances have a fixed composition and distinct properties. Carbon dioxide and sugar are compounds, while iron and oxygen are elements and all of them are pure. Water is not an element; it is a compound, so the first option is wrong. Air is a uniform mixture so the option (iv) is also incorrect.
Question 5. Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved in the above reactions as elements, compounds or mixtures, with justification.
Answer:
The reaction of iron will be written as
Iron + Oxygen + Water (moisture) → Iron oxide (rust)
For magnesium,
Magnesium + Oxygen → Magnesium oxide
So, iron and magnesium are elements, as they are made of only one kind of atom. But iron oxide and magnesium oxide are compounds as they are formed when elements react chemically with oxygen. These new substances have different properties than the elements they are made from.
Question 6. 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.
Elements
| Compounds | Mixtures |
| | |
| | |
Identify pure substances amongst these and list them below
Answer:
Table 8.3
Elements
|
Compounds
|
Mixtures
|
Aluminium, Gold, Oxygen, Nitrogen, Sulfur, Hydrogen
|
Water, Glucose, Carbon dioxide, Sodium chloride, Baking soda, Magnesium oxide, rust and Iron sulfide
|
Sand, Seawater, Muddy water, Air, Fruit juice
|
Pure substances have uniform and definite composition and properties. So, here the pure substances are carbon dioxide, iron, oxygen, glucose, aluminum, gold, water, nitrogen, sodium chloride, sulfur, hydrogen and magnesium oxide.
Question 7. 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:
When iron filings and sulfur powder are heated, they form iron sulfide which is a new compound.
Iron + Sulfur → Iron sulfide
It is different from the mixture because the compound (iron sulfide) has new properties and cannot be separated easily.
Question 8. 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 both an element and a compound at the same time. Elements contain only one type of atom, while compounds are made of two or more elements chemically combined. These are two different categories of matter based on their composition.
Question 9. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?
Answer:
If water were a mixture of oxygen and hydrogen then it would no longer have the same physical and chemical properties. It would be unsafe to drink or use, as hydrogen and oxygen gases do not combine naturally without a spark. Water would not have a fixed boiling point or freezing point like it does now as a compound.
Question 10. Analyze Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Answer:
Here, in this experiment, the gas A is hydrogen. When a metal reacts with acid, it gives a salt with the evolution of hydrogen gas. In this experiment, zinc is a metal which reacts with the acid to give zinc chloride and hydrogen gas.
The equation is as follows-
Zinc + dilute hydrochloric acid → Zinc chloride + Hydrogen
Question 11. Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.
Answer:
The two compounds that are made from non-metals only are carbon dioxide and sulfur dioxide.
Carbon dioxide (CO2)
It is used in fire extinguishers.
It is used in cold drinks or soda water.
Sulfur dioxide (SO2)
It is used as a preservative to prevent the staling of food.
It is used as a disinfectant to heal the wounds.
Question 12. How can gold be classified as both a mineral and a metal?
Answer:
Gold is found naturally in the Earth as a mineral in rocks. After extraction and purification, it becomes a shiny, soft metal used in jewelry and electronics. So, in nature, it is a mineral but in refined form, it is a metal.
Approach to Solve Chapter 8 Questions Effectively
To solve class 8 science chapter 8 nature of matter: elements, compounds, and mixtures question answer effectively, it is very important to follow a structured approach. Given below are the approaches to solving questions from this chapter:
1. Understand the key concepts first
Before attempting questions, make sure you clearly know the topics, like
- What are elements, compounds, and mixtures?
- The differences between them, e.g., fixed composition, separation methods, and properties.
- Types of mixtures- homogeneous and heterogeneous.
2. Identify the keywords in the question
Look for words like combined, separated, fixed composition, different properties, etc., as they will help you decide whether a substance is an element, compound, or mixture. You can learn these concepts by solving the nature of matter: elements, compounds, and mixtures class 8 question answer.
3. Make notes
You can make use of tables to classify the elements, compounds, and mixtures. This will help you a lot in answering the questions. Also, learn the difference between physical and chemical changes.
4. Practice equations
Practice writing the simple equations like
Magnesium + Oxygen → Magnesium oxide
This will help you answer the reaction-based questions easily. Also, refer to class 8 science chapter 8 nature of matter: elements, compounds, and mixtures solutions to score well in exams.
5. Understand the activities
The activities discussed in the chapter are so important and are often asked in exams. Do practice them attentively.
Also, focus on assertion and reason-type questions, as they are crucial to understanding. Also, practice the chapter 8 questions and answers as well.