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Practice Class 9 Science Chapter 2 – Is Matter Around Us Pure? with 5 NCERT-based MCQs on physical and chemical changes, elements, compounds, mixtures and the differences between pure substances and mixtures.
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Chapter Information
Subject: Science
Class: 9
Chapter: Is Matter Around Us Pure?
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 7
Difficulty Level: Moderate
Based On: NCERT Syllabus
Introduction
Matter can be classified into different categories based on its composition and properties. A substance may be an element, compound or mixture, and these categories have important differences.
A physical change generally does not produce a new substance, whereas a chemical change results in the formation of one or more new substances.
This Practice Set 7 focuses on elements, compounds, mixtures, physical changes and chemical changes and helps students understand the differences between these forms of matter.
What You Will Learn
✔ Elements
✔ Compounds
✔ Mixtures
✔ Physical changes
✔ Chemical changes
✔ Formation of new substances
✔ Fixed and variable composition
✔ Differences between compounds and mixtures
Why This Topic Is Important
Understanding the difference between elements, compounds and mixtures is one of the central concepts of this chapter.
Students also need to distinguish physical changes from chemical changes. These concepts are useful in identifying substances and predicting whether a process results in the formation of a new substance.
5 MCQs with Answers and Detailed Solutions
Q1. Which of the following is an element?
A) Water
B) Carbon dioxide
C) Iron
D) Sodium chloride
Answer: C) Iron
Detailed Solution
An element is a pure substance made up of only one kind of atom.
Iron is an element and is represented by the symbol Fe.
Water, carbon dioxide and sodium chloride are compounds because each contains more than one element chemically combined in a fixed proportion.
Exam Tip
Remember: Element → one kind of atom.
Q2. Which of the following is a compound?
A) Iron
B) Oxygen
C) Water
D) Air
Answer: C) Water
Detailed Solution
A compound is a pure substance formed when two or more elements combine chemically in a fixed proportion.
Water is made up of hydrogen and oxygen chemically combined in a definite ratio. Therefore, water is a compound.
Iron and oxygen are elements, while air is a mixture of gases.
Exam Tip
A compound contains two or more elements chemically combined in a fixed proportion.
Q3. Which statement correctly distinguishes a mixture from a compound?
A) A mixture always has a fixed composition.
B) Components of a mixture are chemically combined.
C) Components of a mixture can generally retain their individual properties.
D) A mixture can contain only two elements.
Answer: C) Components of a mixture can generally retain their individual properties.
Detailed Solution
In a mixture, substances are physically combined and generally retain their individual properties.
The components of a mixture may be present in variable proportions and can often be separated by physical methods.
In contrast, the elements in a compound are chemically combined in a fixed proportion and form a substance with different properties.
Exam Tip
Mixture → physical combination and variable composition.
Q4. Which of the following is a chemical change?
A) Melting of ice
B) Cutting paper
C) Dissolving sugar in water
D) Rusting of iron
Answer: D) Rusting of iron
Detailed Solution
A chemical change results in the formation of one or more new substances.
When iron reacts with oxygen and moisture, it forms rust, which has properties different from those of iron.
Melting ice, cutting paper and dissolving sugar in water do not form a new substance under ordinary conditions.
Exam Tip
If a new substance is formed, the process is generally a chemical change.
Q5. Which of the following is a physical change?
A) Burning of paper
B) Rusting of iron
C) Melting of ice
D) Curdling of milk
Answer: C) Melting of ice
Detailed Solution
A physical change changes the physical state, shape or appearance of a substance without forming a new substance.
When ice melts, it changes from solid water to liquid water. The substance remains water.
Burning paper, rusting iron and curdling milk involve chemical changes and formation of new substances.
Exam Tip
Change of state without formation of a new substance → physical change.
Important Formulas & Concepts
This topic does not involve a major mathematical formula. The following concepts are important.
1. Element
An element is a pure substance made up of only one kind of atom.
Examples: Iron, copper, oxygen.
2. Compound
A compound is a pure substance formed when two or more elements combine chemically in a fixed proportion.
Examples: Water, carbon dioxide, sodium chloride.
3. Mixture
A mixture contains two or more substances physically combined in variable proportions.
4. Physical Change
A physical change does not result in the formation of a new substance.
Example: Melting of ice.
5. Chemical Change
A chemical change results in the formation of one or more new substances.
Examples: Rusting of iron, burning of paper.
6. Key Difference
Mixture: Components are physically combined.
Compound: Elements are chemically combined.
Related Practice Questions
Q1. What is an element?
Q2. What is a compound?
Q3. How is a mixture different from a compound?
Q4. What is a physical change?
Q5. What is a chemical change?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which one is an element?
A) Water
B) Iron
C) Carbon dioxide
D) Sodium chloride
Q2. Which one is a compound?
A) Copper
B) Oxygen
C) Water
D) Air
Q3. Which process is a chemical change?
A) Melting ice
B) Cutting paper
C) Rusting iron
D) Dissolving sugar
Q4. Which process is a physical change?
A) Burning wood
B) Rusting iron
C) Curdling milk
D) Melting ice
Q5. Components of a mixture are generally:
A) Chemically combined in a fixed ratio
B) Physically combined and retain many of their properties
C) Always present in equal amounts
D) Converted into a new element
Exam Tips
✔ Learn the definitions of element, compound and mixture.
✔ Remember that compounds have a fixed composition.
✔ Remember that mixtures can have variable composition.
✔ Focus on whether a new substance is formed when identifying a chemical change.
✔ Learn common examples of physical and chemical changes.
✔ Do not confuse a compound with a mixture.
Quick Revision Notes
✔ Element: Pure substance made of one kind of atom.
✔ Compound: Pure substance formed by chemical combination of elements in a fixed proportion.
✔ Mixture: Two or more substances physically combined.
✔ Physical change: No new substance is formed.
✔ Chemical change: One or more new substances are formed.
✔ Iron: Element.
✔ Water: Compound.
✔ Air: Mixture.
✔ Rusting: Chemical change.
✔ Melting ice: Physical change.
Common Mistakes Students Make
❌ Thinking air is a compound.
❌ Thinking water is an element.
❌ Confusing a mixture with a compound.
❌ Assuming every change of appearance is a chemical change.
❌ Forgetting that formation of a new substance is an important sign of a chemical change.
❌ Thinking all mixtures have fixed composition.
Key Takeaways
✔ Elements are pure substances made of one kind of atom.
✔ Compounds contain elements chemically combined in fixed proportions.
✔ Mixtures contain substances physically combined.
✔ Mixtures generally have variable composition.
✔ Physical changes do not form new substances.
✔ Chemical changes result in new substances.
✔ Rusting of iron is a chemical change.
✔ Melting of ice is a physical change.
FAQs
Q. What is an element?
Answer:
An element is a pure substance made up of only one kind of atom.
Q. What is a compound?
Answer:
A compound is a pure substance formed when two or more elements chemically combine in a fixed proportion.
Q. What is a mixture?
Answer:
A mixture is formed when two or more substances are physically combined in variable proportions.
Q. What is a physical change?
Answer:
A physical change changes the physical properties or state of a substance without forming a new substance.
Q. What is a chemical change?
Answer:
A chemical change results in the formation of one or more new substances with different properties.
Q. Is air a mixture or a compound?
Answer:
Air is a mixture of gases, not a compound.
Conclusion
Class 9 Science Chapter 2 – Is Matter Around Us Pure? focuses on elements, compounds, mixtures, physical changes and chemical changes.
Understanding these differences is essential for correctly classifying substances and identifying the nature of different changes. These concepts also provide a foundation for further study of matter and its composition.
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