Matter in Our Surroundings Important Questions
Matter is everything that occupies space and possesses mass. Every object that we see, touch or use in our daily life, whether it is a chair, a pencil, water, air, milk, soil or even the human body, is made of matter. Although matter appears different in shape, size and appearance, it is fundamentally composed of extremely tiny particles that are continuously moving. The arrangement, movement and attraction between these particles determine whether matter exists as a solid, liquid or gas.
The following important questions have been carefully designed according to the latest Class 9 Science syllabus. They cover conceptual understanding, objective questions, application-based questions and examination-oriented descriptive questions. Every answer remains hidden behind a Show Answer button so that students can first attempt the question independently before checking the correct explanation.
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Multiple Choice Questions (MCQs)
1. Which of the following is considered matter?
- A. Heat
- B. Light
- C. Air
- D. Sound
Answer: C. Air
Explanation: Air occupies space and has mass. Since anything that has mass and occupies space is called matter, air is considered matter. Heat, light and sound are forms of energy and therefore are not matter.
2. Which statement correctly describes the particles of matter?
- A. They remain completely at rest.
- B. They are continuously moving.
- C. They exist only in liquids.
- D. They have no mass.
Answer: B. They are continuously moving.
Explanation: The particles of matter are always in motion because they possess kinetic energy. The speed of movement increases with an increase in temperature.
3. Which state of matter has both a definite shape and a definite volume?
- A. Liquid
- B. Gas
- C. Solid
- D. Plasma
Answer: C. Solid
Explanation: In solids, the particles are packed very closely together with strong intermolecular forces. Therefore, solids maintain both their shape and volume.
4. Diffusion occurs fastest in which state of matter?
- A. Solid
- B. Liquid
- C. Gas
- D. All three at the same rate
Answer: C. Gas
Explanation: Gas particles have maximum kinetic energy and very large intermolecular spaces. Therefore, they move rapidly and diffuse much faster than solids or liquids.
5. Which process converts a liquid into vapour below its boiling point?
- A. Condensation
- B. Evaporation
- C. Freezing
- D. Melting
Answer: B. Evaporation
Explanation: Evaporation takes place from the surface of a liquid at every temperature. It does not require the liquid to reach its boiling point.
6. What is the SI unit of temperature?
- A. Degree Celsius
- B. Fahrenheit
- C. Kelvin
- D. Joule
Answer: C. Kelvin
Explanation: Kelvin is the internationally accepted SI unit of temperature used in scientific measurements.
7. Which process changes a gas into a liquid?
- A. Sublimation
- B. Evaporation
- C. Condensation
- D. Fusion
Answer: C. Condensation
Explanation: During condensation, gas particles lose heat, move closer together and convert into the liquid state.
8. Which factor increases the rate of evaporation?
- A. High humidity
- B. Low temperature
- C. Strong wind
- D. Smaller surface area
Answer: C. Strong wind
Explanation: Wind removes water vapour present above the liquid surface, allowing more liquid particles to escape into the air. This increases the rate of evaporation.
9. Dry ice is the solid form of which substance?
- A. Oxygen
- B. Nitrogen
- C. Carbon dioxide
- D. Hydrogen
Answer: C. Carbon dioxide
Explanation: Dry ice is solid carbon dioxide. It changes directly from solid to gas without becoming a liquid, a process known as sublimation.
10. Which property of matter is responsible for keeping the particles together?
- A. Reflection
- B. Refraction
- C. Intermolecular force of attraction
- D. Magnetism
Answer: C. Intermolecular force of attraction
Explanation: The particles of matter attract one another through intermolecular forces. The strength of this attraction determines whether the substance exists as a solid, liquid or gas.
True or False
Read each statement carefully and determine whether it is True or False. Think about the concept before revealing the answer.
1. Matter is made up of extremely tiny particles.
Answer: True
Explanation: Every substance around us consists of microscopic particles called particles of matter. These particles are so small that they cannot be seen with the naked eye.
2. The particles of matter remain completely at rest.
Answer: False
Explanation: Particles of matter are always in continuous motion because they possess kinetic energy. Their movement becomes faster as temperature increases.
3. Solids have a definite shape and a definite volume.
Answer: True
Explanation: The particles in solids are tightly packed and held together by strong intermolecular forces, giving solids a fixed shape and fixed volume.
4. Diffusion occurs only in gases.
Answer: False
Explanation: Diffusion takes place in solids, liquids and gases. However, it is fastest in gases because their particles move freely and rapidly.
5. Liquids have a fixed volume but no fixed shape.
Answer: True
Explanation: Liquids take the shape of the container in which they are kept while maintaining a constant volume.
6. Evaporation takes place only at the boiling point.
Answer: False
Explanation: Evaporation occurs at every temperature from the surface of a liquid, whereas boiling occurs only at the boiling point.
7. Increasing the surface area increases the rate of evaporation.
Answer: True
Explanation: A larger surface area exposes more liquid particles to the surroundings, allowing more particles to escape into the air.
8. Dry ice is solid carbon dioxide.
Answer: True
Explanation: Dry ice is the solid form of carbon dioxide. It changes directly from solid to gas through sublimation.
9. Kelvin is the SI unit of temperature.
Answer: True
Explanation: Scientists use Kelvin as the standard SI unit for measuring temperature.
10. Gases cannot be compressed.
Answer: False
Explanation: Gases are highly compressible because there are large empty spaces between their particles.
Fill in the Blanks
Fill in each blank with the most appropriate word or phrase. These questions are frequently asked in school examinations and help strengthen your understanding of important concepts from the chapter.
1. Matter occupies ________ and has mass.
Answer: Space
Explanation: One of the basic characteristics of matter is that it occupies space and possesses mass.
2. The process in which a solid changes directly into a gas without passing through the liquid state is called ________.
Answer: Sublimation
Explanation: Substances such as camphor, naphthalene balls and dry ice undergo sublimation.
3. The SI unit of temperature is ________.
Answer: Kelvin
Explanation: Kelvin is the internationally accepted SI unit used for measuring temperature.
4. The process of converting a liquid into vapour below its boiling point is known as ________.
Answer: Evaporation
Explanation: Evaporation is a surface phenomenon that occurs at all temperatures.
5. The force that keeps the particles of matter together is called the ________ force.
Answer: Intermolecular
Explanation: Intermolecular force of attraction holds the particles together and determines the physical state of matter.
6. Gas particles have very ________ spaces between them.
Answer: Large
Explanation: The large intermolecular spaces present in gases make them highly compressible.
7. Under normal atmospheric pressure, ice melts at ________ °C.
Answer: 0
Explanation: At standard atmospheric pressure, the melting point of ice is 0°C or 273 K.
8. Increasing the ________ area of a liquid increases the rate of evaporation.
Answer: Surface
Explanation: A larger surface area exposes more particles to the atmosphere, allowing faster evaporation.
9. The process of converting a gas into a liquid is called ________.
Answer: Condensation
Explanation: During condensation, gas particles lose heat and come closer together to form a liquid.
10. During diffusion, particles move from a region of ________ concentration to a region of lower concentration.
Answer: Higher
Explanation: Diffusion is the natural movement of particles from an area of higher concentration to an area of lower concentration until equilibrium is achieved.
Match the Following
Match the items in Column A with the most appropriate option in Column B. This exercise helps you revise the important processes related to changes in the state of matter.
| Column A | Column B |
|---|---|
| A. Melting | 1. Gas changes into Liquid |
| B. Condensation | 2. Liquid changes into Gas |
| C. Evaporation | 3. Solid changes into Liquid |
| D. Sublimation | 4. Solid changes directly into Gas |
| E. Freezing | 5. Liquid changes into Solid |
Correct Matching:
- A → 3 (Melting – Solid changes into Liquid)
- B → 1 (Condensation – Gas changes into Liquid)
- C → 2 (Evaporation – Liquid changes into Gas)
- D → 4 (Sublimation – Solid changes directly into Gas)
- E → 5 (Freezing – Liquid changes into Solid)
Explanation: These five processes describe the different ways in which matter changes from one physical state to another by either gaining or losing heat energy.
Assertion and Reason
Read the following Assertion (A) and Reason (R) carefully and choose the correct option.
- A. Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.
- B. Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
- C. Assertion is true, but Reason is false.
- D. Assertion is false, but Reason is true.
1. Assertion (A): Diffusion occurs fastest in gases.
Reason (R): Gas particles possess high kinetic energy and have large intermolecular spaces.
Answer: A. Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.
Explanation: Gas particles move freely and rapidly because they have maximum kinetic energy and large spaces between them. Therefore, diffusion is much faster in gases than in solids or liquids.
2. Assertion (A): Evaporation produces a cooling effect.
Reason (R): During evaporation, the particles with higher kinetic energy escape from the surface by absorbing heat from the surroundings.
Answer: A. Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.
Explanation: The escaping particles carry away heat energy, leaving behind particles with lower average kinetic energy. As a result, the remaining liquid becomes cooler.
3. Assertion (A): Solids are highly compressible.
Reason (R): The particles in solids are packed very closely together.
Answer: D. Assertion is false, but Reason is true.
Explanation: Since the particles of solids are tightly packed with almost no empty space, solids cannot be compressed easily.
4. Assertion (A): Boiling occurs only at a fixed temperature for a given pressure.
Reason (R): During boiling, vapour formation takes place throughout the entire liquid.
Answer: B. Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
Explanation: Boiling indeed occurs at a fixed temperature, and bubbles are formed throughout the liquid. However, this does not explain why the boiling point remains fixed for a particular pressure.
5. Assertion (A): Increasing humidity increases the rate of evaporation.
Reason (R): Humid air already contains a large amount of water vapour.
Answer: D. Assertion is false, but Reason is true.
Explanation: Since humid air already contains a high amount of water vapour, it cannot easily accommodate more vapour. Therefore, the rate of evaporation decreases as humidity increases.
Very Short Answer Questions
Answer the following questions in one or two sentences. These questions are designed to test your understanding of the fundamental concepts of the chapter. Write the answers in your own words wherever possible.
1. What is matter?
Answer: Matter is anything that has mass and occupies space. Everything around us, such as air, water, soil, books, furniture, and living organisms, is made up of matter.
2. Define diffusion.
Answer: Diffusion is the spontaneous movement of particles from a region of higher concentration to a region of lower concentration until they become uniformly distributed.
3. What is evaporation?
Answer: Evaporation is the process by which a liquid changes into vapour from its surface at any temperature below its boiling point.
4. What is latent heat of fusion?
Answer: Latent heat of fusion is the amount of heat required to convert one kilogram of a solid into a liquid at its melting point without changing its temperature.
5. Mention any two factors that increase the rate of evaporation.
Answer: Any two of the following:
- Increase in temperature
- Increase in surface area
- Increase in wind speed
- Decrease in humidity
Short Answer Questions
Answer the following questions in about 40–70 words. Write your answers in a clear and systematic manner. Wherever possible, support your explanation with suitable examples from everyday life.
1. Explain any four characteristics of particles of matter.
Answer:
The particles of matter have the following important characteristics:
- They are extremely tiny in size and cannot be seen with the naked eye.
- There are spaces between the particles, which allow substances to mix with one another.
- The particles are in continuous random motion because they possess kinetic energy.
- They attract one another through intermolecular forces, and the strength of this attraction varies in solids, liquids and gases.
These properties explain why matter exists in different physical states and why changes of state are possible.
2. Differentiate between evaporation and boiling.
Answer:
| Evaporation | Boiling |
|---|---|
| Occurs at all temperatures. | Occurs only at the boiling point. |
| Takes place only from the surface of the liquid. | Takes place throughout the liquid. |
| It is a slow process. | It is a comparatively rapid process. |
| Produces cooling. | Mainly changes the state of matter. |
3. Why are gases highly compressible?
Answer:
Gas particles are located far apart from one another and have very large intermolecular spaces. When pressure is applied, these empty spaces decrease and the particles come closer together. Therefore, gases can be compressed easily and stored in cylinders such as LPG and CNG cylinders.
4. Explain why evaporation causes cooling.
Answer:
During evaporation, the particles having higher kinetic energy escape from the surface of the liquid after absorbing heat from the surroundings. As these energetic particles leave, the average kinetic energy of the remaining particles decreases, causing the liquid and its surroundings to become cooler. This is why sweating cools our body.
5. Explain the effect of temperature on the movement of particles of matter.
Answer:
When temperature increases, the particles of matter gain kinetic energy and move faster. Their movement becomes more vigorous, reducing the effect of intermolecular forces. As a result, solids may melt into liquids and liquids may change into gases. Similarly, lowering the temperature reduces the kinetic energy of particles and brings them closer together.
Long Answer Questions
Answer the following questions in detail. These questions require conceptual understanding, scientific reasoning, suitable examples, and well-organized explanations. Such questions are frequently asked in school examinations and help develop a deeper understanding of the chapter.
1. Explain the characteristics of particles of matter with suitable examples.
Answer:
Matter is composed of extremely tiny particles that possess several unique characteristics. These characteristics help us understand the behaviour of solids, liquids, and gases in everyday life.
- Particles of matter are extremely small: The particles are so tiny that they cannot be seen with the naked eye. For example, a few crystals of potassium permanganate can colour a large quantity of water, showing that one crystal contains millions of tiny particles.
- Particles of matter have spaces between them: There are empty spaces between the particles. When sugar or salt is added to water, its particles occupy these spaces without significantly increasing the water level.
- Particles of matter are continuously moving: Matter particles possess kinetic energy and remain in constant random motion. This movement increases with temperature. The spreading of perfume in a room is a common example of moving particles.
- Particles of matter attract one another: A force of attraction exists between the particles. This force is strongest in solids, weaker in liquids, and weakest in gases, giving each state of matter its unique properties.
These characteristics explain why matter exists in different physical states and why substances can undergo changes such as melting, boiling, evaporation and condensation.
2. Compare solids, liquids and gases on the basis of the particle theory of matter.
Answer:
The three states of matter differ because of the arrangement, movement and attraction between their particles.
| Property | Solids | Liquids | Gases |
|---|---|---|---|
| Particle Arrangement | Very closely packed | Moderately packed | Far apart |
| Force of Attraction | Very strong | Moderate | Very weak |
| Shape | Fixed | No fixed shape | No fixed shape |
| Volume | Fixed | Fixed | No fixed volume |
| Compressibility | Negligible | Very little | Very high |
| Diffusion | Slowest | Moderate | Fastest |
Thus, the difference in particle arrangement and intermolecular force explains the physical properties of the three states of matter.
3. Explain the change of state of matter with the help of heating and cooling.
Answer:
The physical state of matter changes when heat energy is either supplied or removed. These changes occur because heating and cooling affect the kinetic energy of particles.
When a solid is heated, its particles gain kinetic energy and begin to vibrate more vigorously. At the melting point, the particles overcome some of the intermolecular forces and the solid changes into a liquid. This process is called melting.
On further heating, the liquid particles move even faster. At the boiling point, they gain sufficient energy to completely overcome the intermolecular forces and change into vapour. This process is known as boiling or vaporisation.
When the vapour is cooled, it loses kinetic energy and changes back into a liquid through condensation. Further cooling causes the liquid particles to lose more energy, resulting in freezing, where the liquid becomes a solid.
During melting and boiling, the supplied heat is used to overcome the force of attraction between particles rather than increasing temperature. This energy is known as latent heat. Thus, changes in temperature and pressure enable matter to change from one state to another.
4. Explain the factors affecting evaporation with suitable examples.
Answer:
Evaporation is a surface phenomenon that depends upon several environmental factors. The important factors are explained below:
- Surface Area: A larger surface exposes more liquid particles to the atmosphere, increasing evaporation. Water spread on a floor dries faster than water collected in a bucket.
- Temperature: Higher temperature increases the kinetic energy of particles, enabling more particles to escape from the liquid surface. Clothes dry faster on sunny days than on cold days.
- Humidity: High humidity slows evaporation because the surrounding air already contains a large amount of water vapour. Therefore, clothes dry slowly during the rainy season.
- Wind Speed: Fast-moving air removes water vapour from the liquid surface, allowing continuous evaporation. Clothes dry quickly on windy days.
Understanding these factors helps explain many everyday situations such as drying clothes, cooling by sweating, and the working of desert coolers.
5. Explain the cooling effect of evaporation with suitable daily-life examples.
Answer:
Evaporation is accompanied by cooling because the particles that escape from the surface possess higher kinetic energy. These energetic particles absorb heat from the liquid as well as from the surroundings before escaping into the air. Consequently, the average kinetic energy of the remaining particles decreases, lowering the temperature of the liquid and its surroundings.
This cooling effect can be observed in many everyday situations:
- Sweat evaporates from our skin, absorbing body heat and keeping us cool during summer.
- Water stored in an earthen pot remains cool because water continuously evaporates through tiny pores in the pot.
- When alcohol or spirit is applied to the skin, it evaporates rapidly and produces a cooling sensation.
- Desert coolers work on the principle of evaporation. As water evaporates from the cooling pads, it absorbs heat from the incoming air, making the air cooler.
- People sprinkle water on the roofs of houses during hot weather because the evaporating water removes heat and lowers the temperature.
Thus, evaporation is an important natural cooling process that plays a significant role in daily life, weather, and various cooling technologies.
Case-Based Questions
Read each case carefully and answer the questions that follow. These questions are designed to test your ability to apply scientific concepts to real-life situations. Read the passage thoroughly before attempting the questions.
Case Study 1: Drying of Wet Clothes
After washing his school uniform, Rahul spread the clothes on a clothesline in the open sunlight. There was a gentle breeze blowing throughout the afternoon. His sister noticed that the clothes became completely dry within a few hours. The next day, when similar clothes were washed and kept indoors on a rainy day, they took much longer to dry. Rahul explained that the surrounding weather conditions directly affect the rate at which water changes into vapour.
Questions:
- Which process is responsible for drying wet clothes?
- Name any three factors responsible for the faster drying of clothes on a sunny day.
- Why do clothes dry slowly during the rainy season?
- Why does wind speed affect the drying of clothes?
Answer:
The drying of wet clothes occurs due to evaporation. During evaporation, water molecules present on the surface of the clothes absorb heat energy from the surroundings and escape into the atmosphere in the form of water vapour.
Clothes dry much faster on a sunny day because:
- High temperature increases the kinetic energy of water molecules.
- Strong sunlight provides sufficient heat for rapid evaporation.
- Moving air or wind continuously removes water vapour from around the clothes.
- The surrounding air usually has lower humidity than during the rainy season.
During the rainy season, the atmosphere already contains a large amount of water vapour. Since the air is highly humid, it cannot easily accept more vapour from the clothes. As a result, evaporation becomes slow and the clothes take longer to dry.
Wind also plays an important role because it removes moist air surrounding the clothes and replaces it with dry air. This allows evaporation to continue at a faster rate.
Case Study 2: Smell of Perfume
A teacher sprayed perfume near the classroom door before the lecture began. Within a few seconds, students sitting in the last row could also smell the fragrance. Even though the perfume was sprayed only in one corner, the smell spread throughout the classroom without anyone carrying it from one place to another.
Questions:
- Which property of matter explains this observation?
- Why does the smell spread rapidly in air?
- What does this observation tell us about the particles of matter?
- Would this process occur faster in gases or liquids? Give a reason.
Answer:
This phenomenon is explained by the process of diffusion. Diffusion is the spontaneous movement of particles from a region of higher concentration to a region of lower concentration until they become uniformly mixed.
The smell spreads rapidly because gas particles possess very high kinetic energy and move continuously in all directions. They also have large intermolecular spaces, allowing them to travel freely throughout the room.
This observation proves that:
- Particles of matter are continuously moving.
- There are spaces between the particles.
- Particles mix with one another on their own.
The process occurs much faster in gases than in liquids because gas particles move more rapidly and experience much weaker intermolecular forces.
Case Study 3: Storage of LPG
Liquefied Petroleum Gas (LPG) is widely used for cooking in homes. It is stored inside strong steel cylinders under high pressure. When the regulator is opened, the gas comes out quickly and mixes with the surrounding air. Safety instructions advise users to close the cylinder valve after use and ensure proper ventilation in the kitchen.
Questions:
- Why can LPG be stored inside cylinders under pressure?
- Why does LPG spread quickly after the regulator is opened?
- Which property of gases makes them highly compressible?
- State one safety precaution while using LPG.
Answer:
LPG can be stored inside cylinders because gases have very large intermolecular spaces. When high pressure is applied, these spaces decrease considerably, allowing a large quantity of gas to be stored in a comparatively small container.
Once the regulator is opened, the pressure inside the cylinder decreases. The gas expands rapidly and diffuses into the surrounding air because its particles move continuously with high kinetic energy.
Gases are highly compressible because:
- The particles are far apart.
- Large empty spaces exist between them.
- The intermolecular force of attraction is very weak.
One important safety precaution is to keep the cylinder valve closed when it is not in use and ensure proper ventilation in the kitchen so that leaked gas does not accumulate.
Practice Tips
- Learn all important definitions such as matter, diffusion, evaporation, boiling, condensation, sublimation and latent heat.
- Understand the differences between solids, liquids and gases using particle arrangement and intermolecular forces.
- Revise all factors affecting evaporation with practical examples.
- Practice writing scientific reasons instead of memorising one-line answers.
- Attempt the questions without revealing the answers first to improve conceptual understanding.
- Revise diagrams and state-change processes regularly for better retention.
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