Matter in Our Surroundings is the opening chapter of Class 9 Science, and it lays the foundation for everything you'll study about physical and chemical changes for the rest of the year. These NCERT solutions class 9 science chapter 1 walk through every in-text and end-of-chapter question with clear, exam-ready explanations.
Whether you're revising for a unit test or preparing for the board exam, this guide follows the exact order of the NCERT textbook so you can check your work chapter-section by chapter-section. For more on this topic, you can also read our detailed chapter notes.
Quick Recap: What This Chapter Covers
Before the exercises, here's a quick refresher: matter is anything with mass that occupies space. This chapter covers the particle nature of matter, the three states of matter (solid, liquid, gas), diffusion, changes of state, latent heat, and evaporation.
In-Text Questions (Section 1.1: Physical Nature of Matter)
Question 1: Which of the following are pure substances? Ice, milk, iron, hydrochloric acid, calcium oxide, mercury, brick, wood, air.
Solution: Ice, iron, hydrochloric acid, calcium oxide, and mercury are pure substances - each has a fixed composition and consists of only one kind of particle. Milk, brick, wood, and air are mixtures, since they are made up of two or more substances mixed together in variable proportions.
Question 2: Which of the following will show "Tyndall effect"? Salt solution, milk, copper sulphate solution, starch solution.
Solution: Milk and starch solution show the Tyndall effect. Both are colloids, meaning their particle size is large enough to scatter a beam of light passing through them. Salt solution and copper sulphate solution are true solutions with much smaller particles that don't scatter light.
Question 3: Classify the following as chemical or physical changes: cutting of trees, melting of butter in a pan, rusting of almirah, boiling of water to form steam, passing of electric current through water and the water breaking down into hydrogen and oxygen gas, dissolving common salt in water, making a fruit salad with raw fruits, burning of paper and wood.
Solution:
- Physical changes: cutting of trees, melting of butter, boiling of water to form steam, dissolving common salt in water, making a fruit salad
- Chemical changes: rusting of almirah, electrolysis of water into hydrogen and oxygen, burning of paper and wood
A physical change doesn't produce a new substance and is generally reversible, while a chemical change forms a new substance and is usually irreversible.
In-Text Questions (Section 1.2: Characteristics of Particles of Matter)
Question: A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Solution: This shows that particles of matter (water) have spaces between them and are held together by relatively weak forces of attraction, which allows objects to move through the water.
Question: What are the characteristics of particles of matter?
Solution: Particles of matter have three key characteristics: (1) they have spaces between them, (2) they are continuously moving (they possess kinetic energy), and (3) they attract each other.
Exercise 1.1: States of Matter
Question: Convert the following temperatures to the Celsius scale: (a) 300 K (b) 573 K
Solution:
- (a) 300 K − 273 = 27°C
- (b) 573 K − 273 = 300°C
Question: What is the physical state of water at: (a) 25°C (b) 0°C (c) 100°C?
Solution:
- (a) At 25°C, water exists as a liquid
- (b) At 0°C, water exists as solid ice, and as liquid water - this is the melting point, where both states can coexist
- (c) At 100°C, water exists as liquid water and water vapour (gas) - this is the boiling point, where both states can coexist
Question: Give two reasons to justify: (a) water at room temperature is a liquid (b) an iron almirah is a solid at room temperature.
Solution:
- (a) Water at room temperature (around 25°C) is above its melting point (0°C) and below its boiling point (100°C), so it exists in the liquid state. Its particles have moderate intermolecular forces - strong enough to keep a fixed volume, but weak enough to let it flow and take the shape of its container.
- (b) An iron almirah remains solid at room temperature because room temperature is far below iron's melting point (about 1,535°C). The particles in iron are held by very strong forces of attraction in fixed positions, giving it a definite shape and volume that doesn't change.
Question: Why is ice at 273 K more effective in cooling than water at the same temperature?
Solution: Ice at 273 K carries extra energy in the form of latent heat of fusion. When ice melts, it absorbs this latent heat from its surroundings without any change in its own temperature. Water at the same temperature doesn't have this extra heat-absorbing phase change available, so ice cools more effectively than water at the same temperature.
Exercise 1.2: Evaporation
Question: Why does a desert cooler cool better on a hot dry day?
Solution: On a hot, dry day, the surrounding air has high temperature and low humidity. Water sprinkled on the cooler's pads evaporates quickly because dry air can absorb more water vapour, and higher temperature gives water particles more energy to escape. Faster evaporation means faster cooling of the surrounding air. On a humid day, the air is already close to saturation, so evaporation - and cooling - slows down.
Question: How does water kept in an earthen pot (matka) become cool during summer?
Solution: An earthen pot has tiny pores in its walls. Water slowly seeps through these pores to the outer surface and evaporates there. Since evaporation causes cooling, this steady evaporation from the outer surface keeps the remaining water inside the pot cool.
Question: Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Solution: Acetone, petrol, and perfume are all volatile liquids with low boiling points, so they evaporate very quickly at room temperature. As they evaporate, they absorb latent heat from our palm to convert from liquid to vapour, which lowers the temperature of the skin and produces the cooling sensation.
Question: Why are we able to sip hot tea or milk faster from a saucer than from a cup?
Solution: A saucer has a much larger surface area than a cup for the same amount of liquid. Since evaporation - and the resulting cooling - happens faster over a larger surface area, tea or milk cools down more quickly in a saucer, letting us sip it sooner without burning our tongue.
Question: What type of clothes should we wear in summer?
Solution: We should wear light-coloured cotton clothes in summer. Cotton is a good absorber of sweat and allows it to evaporate quickly, which cools the body. Light colours reflect heat rather than absorbing it, keeping the body cooler than dark-coloured clothing would.
Tips to Score Full Marks in Chapter 1
- Learn the three characteristics of particles of matter (spaces between particles, constant motion, mutual attraction) - these come up repeatedly across different question types.
- Always convert temperatures correctly: Kelvin = Celsius + 273. Many students lose marks on simple arithmetic slips here.
- Practice explaining evaporation-based questions with all four factors - surface area, temperature, humidity, and wind speed - even if the question only asks about one, mentioning the others shows complete understanding.
- Use the correct terms: don't confuse melting point with boiling point, or evaporation with boiling - they're commonly tested as trick questions.
For more chapter-wise revision, browse our complete set of Class 9 Science notes or try a free practice quiz on this chapter to test yourself with instant scoring.
Frequently Asked Questions
What is the weightage of "Matter in Our Surroundings" in the Class 9 Science exam?
This chapter is foundational and typically contributes to a mix of 1-mark conceptual questions and 2-3 mark questions on evaporation, states of matter, and latent heat, usually totaling around 4-6 marks in unit tests and the annual exam.
What is the difference between evaporation and boiling?
Evaporation is a surface phenomenon that occurs slowly at any temperature below the boiling point, while boiling occurs throughout the liquid at a fixed temperature (the boiling point) with visible bubble formation.
Why does ice float on water?
When water freezes into ice, its molecules arrange into a cage-like crystal structure with more empty space between them than in liquid water. This makes ice less dense than liquid water, so it floats.
Is this chapter only about physical changes, or does it cover chemical changes too?
The chapter briefly distinguishes physical changes (like melting or dissolving) from chemical changes (like rusting or burning) as part of classifying matter, but the main focus is on the physical nature and states of matter - detailed chemical reactions are covered in later chapters.
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