Class 9 Science Chapter 1, "Matter in Our Surroundings," helps students understand key concepts related to the physical and chemical nature of matter and evaporation. The NCERT Solutions for this chapter strictly follow the latest syllabus, ensuring comprehensive coverage of all topics.
These solutions are highly beneficial for exam preparation. They provide detailed explanations and help students develop strong problem-solving skills. By practising these questions and answers, students can effectively cover the entire syllabus and feel more confident during exams.
Using these resources, students can enhance their understanding and improve their performance in the NCERT Solutions Class 9 Science exams.
Here, you can find the link to the PDF of NCERT Solutions Class 9 Science Chapter 1. It contains solutions along with explanations for all topics so that each concept is better understood.
Ans. A :Fusion B :Vaporization C :Condensation D :Solidification E :Sublimation F :De-sublimation/ deposition.
Multiple choice questions
(1) (i) - a, (ii) - b, (iii) - c, (iv) - d (2) (i) - c, (ii) - d, (iii) - b, (iv) - a (3) (i) - c, (ii) - d, (iii) - a, (iv) - b (4) (i) - a, (ii) - d, (iii) - b, (iv) - c
Fill in the blanks
Crossword puzzle
Across (1) Process in which solid changes into liquid. (3) SI unit of temperature. (4) Spreading of smell of cake being baked throughout the house. (6) SI unit of pressure.
Down (2) The solid changes into vapour directly. (5) SI unit of mass (7) Cooking gas
Multiple choice questions
Fill in the blanks
True or False
Crossword puzzle
Very short answer type questions
Short answer type questions
Long answer type questions
(a) What is the physical state of the substance at the points and D ? (b) What is the melting point of the substance? (c) What is its boiling point? (d) What happens to the temperature while the substance is changing state? (e) The substance is not water. How can you judge from the graph?
(i) Out of solids, liquids and gases, which one has
(a) maximum movement of particles
(b) maximum interparticle forces of attraction
(c) minimum spaces in between constitute particles
(ii) How will you demonstrate that particles of matter attract each other?
(i) sugar is added to water with constant stirring
(ii) Naphthalene balls kept in stored warm clothes.
(iii) Ice melts
(ii) As compared to solids liquids are lighter, why?
(iii) Which property of gas is utilized when natural gas is used in vehicles?
(iv) Give two uses of gases in compressed form.
(ii) How will you demonstrate that particles of matter have spaces between them?
Multiple choice questions
Everything in this universe can be organised around two concepts, matterand energy.
2. Option (1)
The perception of joy, love, hate thought, cold, hot, pain is not considered as matter.
3. Option (1)
Diffusion is the process where molecules from a material move from an area of high concentration to an area of low concentration. Thus, ink spreads from its high concentration to a lower concentration area (beaker of water).
4. Option (3)
Solids have strongest interparticle forces of attraction at the room temperature. Both, iron and chalk are solids at room temperature but iron being stronger than chalk possesses strongest interparticle forces of attraction.
5. Option (1)
Both liquids and gases can flow, thus they are called fluids.
6. Option (4)
The molecules of gas have large intermolecular spaces and kinetic energy. Thus, molecules of gas spread in the entire space of the containing vessel.
7. Option (2)
Gases have maximum compressibility because of their maximum interparticle spaces present between their molecules.
Melting is a process in which a solid substance changes into its liquid state.
The temperature at which a solid melt to become a liquid at the atmospheric pressure is called its melting point.
10. Option (1)
The melting point of ice is 0°C, it may also be written as 273 K.
11. Option (1)
373 °C + 273 = 646 K
12. Option (1)
270 K – 273 K = –3°C
13. Option (3)
Kelvin is the SI unit for measuring temperature.
14. Option (3)
Latent literally means not visible or hidden.
15. Option (2)
The temperature at which a liquid change into a gas or vapour at the atmospheric pressure is called its boiling point.
16. Option (3)
Boiling point of water is 100°C in kelvin scale
100°C + 273 = 373 K
17. Option (3)
Ice at 0°C is more effective in cooling as compared to water at 0°C, as it lacks the latent heat of fusion.
18. Option (1)
When a vapour is cooled by lowering its temperature, its interparticle distance decreases and changes into liquid. This process is known as condensation.
19. Option (4)
The process of converting a solid into gas without undergoing into liquid state is known as sublimation.
20. Option (4)
Dry ice is the solid form of carbon dioxide and used as a cooling agent.
21. Option (1)
Naphthalene converts directly from solid into gas without undergoing into liquid state, thus shows sublimation process.
22. Option (1)
When a vapour is cooled by lowering its temperature, its interparticle distance decreases and changes into liquid. This process is known as condensation.
Option (4)
The process of converting a solid into gas without undergoing into liquid state is known as sublimation.
23. Option (3)
Both increase in surface area as well as increase in temperature increases the rate of evaporation.
24. Option (1)
Rate of evaporation increases with increase in temperature as more number of particle get enough kinetic energy to go into the vapour state.
25. Option (4)
Plasma is a fourth phase of matter, apart from the three; solid, liquid and gas phases.
26. Option (2)
Solids always have definite shape.
Liquids have definite volume but not definite shape, gases neither have definite shape nor volume, plasma are super energetic particles formed by heating and ionizing a gas.
27. Option (1)
Chalk is solid state of matter.
28. Option (2)
Stone has a fixed shape and volume because stone is solid. Solids have fixed shape and fixed volume.
29. Option (2)
Solid have the strongest intermolecular force of attraction. In liquids, it is less than solid but more than gases and in gases, it is very weak.
30. Option (3)
Liquids have a definite volume but indefinite shape. This is because the intermolecular forces of attraction in liquids are quite weak as compared to the solid states.
31. Option (1)
Solids have strongest intermolecular force.
32. Option (2)
Gases are compressible because on applying pressure, the space between the gaseous particles decreases. Therefore, gases can be compressed readily.
33. Option (2)
Solids always have definite shape.
Liquids have definite volume but not definite shape, gases neither have definite shape nor volume, plasma are super energetic particles formed by heating and ionizing a gas.
34. Option (1)
Chalk is solid state of matter.
35. Option (2)
Stone has a fixed shape and volume because stone is solid. Solids have fixed shape and fixed volume.
Option (2)
Solid have the strongest intermolecular force of attraction. In liquids, it is less than solid but more than gases and in gases, it is very weak.
Option (3)
Liquids have a definite volume but indefinite shape. This is because the intermolecular forces of attraction in liquids are quite weak as compared to the solid states.
Option (1)
Solids have strongest intermolecular force.
Option (2)
Gases are compressible because on applying pressure, the space between the gaseous particles decreases. Therefore, gases can be compressed readily.
Option (2)
Gases do not have a fixed shape or volume. The particles are freely moving and they do not have a fixed position.
Option (3)
Gases have no definite shape or volume.
Option (3)
The particles in a gas do not have any particular arrangement and there are very weak forces between them. Molecules can move randomly in all directions.
Option (3)
Gases are highly compressible because the space between the molecules is very large. Its intermolecular force of attraction is less.
Option (1)
LPG stands for liquified petroleum gas. It consists of propane (C3H8) and butane (C4H10) as the major constituents. LPG (propane) is denser than air as compared to CNG (Methane). Which is lighter than air.
Option (4)
Matter changes from one state to another by changing temperature or pressure. We can convert from one state to another by adding or removing energy (heat). i.e. by changing temperature or by changing the pressure.
Option (4)
Freezing is a phase transition in which a liquid turn into a solid when its temperature is lowered to its freezing point.
Option (4)
Boiling is the process by which a liquid turn into a vapour when it is heated to its boiling point.
True or False
False
Smell is not the example of matter.
False
Hunger is not an example of matter.
False
Matter is particulate in nature.
True
Movement of hands through air is possible because air (matter) has spaces between its particles
True
Rate of diffusion increases with rise in temperature
True
Sponge is a solid.
True
Solids have least interparticle space due to strongest attraction forces while gases have maximum interparticle space due to weakest attraction forces.
True
The rate diffusion is highest in gases.
True
Boiling point of water is 100∘C/373 K/212∘F.
False
Evaporation is a surface phenomenon.
Very short answer type questions
The colour of the water becomes blue because of the diffusion of copper sulphate particles placed at the bottom of the beaker containing water. There are millions of tiny particles in just one crystal of copper sulphate which keep on dividing themselves into smaller and smaller particles, hence making the water blue coloured.
A substance that has a definite volume but no definite shape is said to be in the liquid state.
Gases can be easily compressed due to minimum intermolecular forces of attraction.
K−273=∘C
Therefore, (i) 0 K=0−273=−273∘C
(ii) 250 K=250−273=−23∘C
∘C+273=K
Therefore, (i) −273∘C=−273+273=0 K
(ii) −100∘C=−100+273=173 K
(iii) −40∘C=−40+273=233 K
(iv) +30∘C=+30+273=303 K
K−273=∘C
Therefore, (a) 300 K=300−273=27∘C
(b) 573 K=573−273=300∘C
(a) Boiling point: "The temperature at which a liquid change into a gas/ vapour at atmospheric pressure is called its boiling point."
Eg. Boiling point of water is 100∘C
(b) Melting point: "The temperature at which a solid melt to become a liquid at atmospheric pressure is called its melting point."
Eg. Melting point of ice is 0∘C
(a) Latent heat of fusion: "The amount of heat energy required to change the state of 1 kg solid into liquid at atmospheric pressure without any change in temperature at its melting point is called as latent heat of fusion." Eg. Latent heat of fusion of ice is 3.34 x 105 J/kg
(b) Latent heat of vaporisation: "The amount of heat energy required to change the state of 1 kg liquid into gas at atmospheric pressure without any change in temperature at its boiling point is called as latent heat of vaporisation."
Eg. Latent heat of vaporisation of water is 22.5×105 J/kg
Increasing the pressure applied and lowering the temperature will help to liquefy a gas.
(1) Decrease in pressure
(2) Increase in temperature
The process of change of state of a substance from solid to gas directly upon heating, without passing through the liquid state, and vice versa upon cooling is called sublimation.
CNG - Compressed Natural Gas; used as fuel in vehicles, automobiles.
LPG - Liquified Petroleum Gas; used as domestic fuel for cooking.
Plasma is the fourth state of matter that consists of super excited and super energetic particles in the form of ionised gases and free electrons.
BEC stands for Bose-Einstein Condensate. It is a gaseous superfluid phase formed by atoms cooled to temperature very near to absolute zero.
Anything that has mass and occupies space is called matter. A matter is made up of tiny particles called atoms. For example, table chair, air, water, honey etc.
Sugar is solid. In solid, particles are very closer to each other so forces of attraction between the particles are also more. Oxygen is gas. In gas, particles are very far from each other, so forces of attraction between the oxygen particles are less.
Short answer type questions
The characteristics of particles of matter are as follows:
(a) The particles of matter have spaces between them.
(b) The particles of matter are continuously moving
(c) The particles of matter are very small.
(d) The particles of matter attract each other.
These characteristics vary from substance to substance and hence results in the existence of three states of matter viz. solid, liquid and gas.
The smell of hot sizzling food reaches us more quickly as compared to the smell of cold food. This is because rate of diffusion is faster at higher temperature than at lower temperature. The rate of diffusion of hot sizzling food is more and hence, reaches you even several metres away. On the other hand, rate of diffusion of cold food is less therefore, you have to go quite close to it in order to get its smell.
(i) Has definite mass, volume and shape - Solid
(ii) Has no definite volume and shape Gas or Plasma
(iii) Has minimum interparticle attraction - Gas
(iv) Has maximum interparticle attraction - Solid
Since the interparticle spaces in the gaseous state particles are very large, they can be changed by altering the amount of pressure applied. Thus, a gas can be compressed to a large extent as
compared to solid which have almost negligible interparticle spaces.
For any substance, the temperature remains constant during the change of state because the heat supplied is used up in changing the state by breaking the intermolecular forces of attraction which hold them together without raising the temperature. This energy which is required to change the state is known as "latent heat".
The temperature of the steam is same as that of the boiling water inside the kettle, but the steam has an additional energy of 22.5×105 J/kg in the form of latent heat of vaporization.
When the incense stick is lighted the heat energy makes the particles of perfume move rapidly. Thus, they easily drift through the air in the room and hence we can smell it anywhere in the room.
Unlike solids, the liquids have fluidity and not rigidity i.e. they have tendency to flow. This is due to lesser interparticle or intermolecular forces that are present in the liquid state as compared to the solid state.
However, the liquids differ in their relative fluidity. For example, water flows at a faster rate than honey because in honey, the particles are heavier and also more closely packed.
The water evaporates rapidly from the hot surface of the road, there by taking away heat from it. Thus, the road becomes cool.
(i) Water keeps cool in the earthen pot(matki) during summer.
When the water oozes out of the pores of an earthen pot, during hot summer, it evaporates rapidly. As the cooling is caused by evaporation, therefore, the temperature of water within the pot falls and hence it becomes cool.
(ii) Rapid cooling of hot tea.
If tea is too hot to sip, we pour it in the saucer. In doing so, we increase the surface area and the rate of evaporation increases. This, in turn, causes cooling and the tea attains a desired temperature for sipping.
Long answer type questions
Diffusion: Spontaneous intermixing of particles of two or more different substances is called diffusion
The rate of diffusion becomes faster with increase in temperature because at higher temperature, the particles have more energy and hence move faster.
Diffusion is,
(i) Fastest between two different gases.
(ii) Slower between two different liquids or a solid and a liquid.
(iii) Slowest (or almost negligible) in case of two different solids.
Example
a. As the drop of ink trickles along the sides of the beaker, the blue colour of the ink starts diffusing in water, which appears like wavy blue streaks in water.
b. The honey drop continues travelling along the side of beaker and there is no visible diffusion of it in water.
c. The ink spreads evenly in the water in about two hours.
Therefore,
Rate of diffusion depends upon the nature of substances.
More viscous substances which have particles with less kinetic energy, takes more time to get diffused.
From these activities it is observed that when two different forms of matter are brought in contact, they intermix spontaneously. This intermixing is possible due to motion of the particles of matter and also due to the spaces between them. The intermixing takes place due to movement of particles of one form into the spaces between the particles of the other form of matter.
(a) A indicates solid state, at point B the substance can be in liquid as well as solid state. At point C substance is in
liquid state while at point D the substance can be in liquid as well as gaseous state.
(b) Melting point of the substance is 15∘C.
(c) Boiling point of the substance is 110∘C.
(d) The temperature remains constant while the substance is changing state.
(e) Pure water has fixed boiling point of 100∘C, whereas this substance is found to have a boiling point of 110∘C. Hence, we can conclude that the substance is not water.
(a) (i) Size of naphthalene balls decreases - Sublimation
(ii) Wax melts in the sun - Melting
(iii) Drying of wet clothes Evaporation
(iv) Formation of clouds Condensation
(v) Mixing of ink into water Diffusion
(b) When we heat a solid, its particles become more energetic and kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating more strongly with greater speed. The energy supplied by heat overcomes the intermolecular forces of attraction between the particles. As a result, the particles leave their mean position and break away from each other. After this solid melt and a liquid is formed. When we supply heat energy to the liquid, the particles of water start vibrating even faster. Some of the particles become so energetic that
they can overcome the attractive forces of the particles around them. Therefore, they become free to move and escape from the liquid. Thus, the liquid evaporates i.e. starts changing into gas.
(c) Diffusion is,
(i) Fastest between two different gases.
(ii) Slower between two different liquids or a solid and a liquid.
(iii) Slowest (or almost negligible) in case of two different solids.
"The process of a liquid changing into vapour (or gas) even below its boiling point is called evaporation."
Whatever be the temperature at which evaporation takes place, the latent heat of vaporization must be supplied whenever a liquid change into vapour (or gas).
Explanation about evaporation: Some particles in a liquid always have more kinetic energy than the others.
So, even when a liquid absorbs heat, below its boiling point, some of its particles have enough energy to overcome the forces of attraction between the particles and escape from the surface of the liquid in the form of vapour (or gas). Thus, the fast-moving particles (or molecules) of a liquid are constantly escaping from the liquid to form vapour (or gas).
Examples
(i) Water in ponds changes from liquid to vapour without reaching the boiling point.
(ii) Water when left uncovered slowly changes into vapour.
(iii) When we put wet clothes for drying, the water from the clothes goes to the atmosphere.
There are five factors which affects the rate of evaporation:
(i) Nature of liquid : Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at faster rate because less energy is required to overcome the attractive forces.
Example : Acetone evaporates faster than water.
(ii) Surface area of the liquid : The evaporation depends upon the surface area. If the surface area is increased, the rate of evaporation increases because the high energy particles from liquid can go into gas phase only through surface.
Example:
(a) The rate of evaporation increases when we put kerosene or petrol in an open China dish than in a test tube.
(b) Clothes dry faster when they are well spread because the surface area for evaporation increases.
(iii) Temperature: Rate of evaporation increases with increase in temperature. This is because with the increase in temperature more number of particles get enough kinetic energy to go into the vapour state (or gaseous state)
Example :
Clothes dry faster in summers than in winters.
(iv) Humidity in the air : The air around us contains water vapour or moisture. The amount of water present in the air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature.
If the humidity is more, the rate of vaporization decreases. The rate of evaporation is more if the air is dry.
Example :
Clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content (humidity) in the air.
(v) Wind speed: The rate of evaporation also increases with increase in speed of the wind. This is because with increase in speed of wind, the particles of water vapour move away with wind in resulting decrease in the amount of vapour in the atmosphere.
Example :
(a) Clothes dry faster on a windy day.
(b) In a desert cooler an exhaust fan sucks the moist air from the cooler chamber which results in greater rate of evaporation of water and hence greater cooling.
(i) (a) Gases have maximum movement of particles since they have maximum space between them.
(b) Solids have maximum interparticle attractions, so they are close to each other.
(c) Solids have minimum space between particles because of the strong force of attraction.
(ii) Aim
Bihu Dancers
To demonstrate the strength of attractive forces between particles of different kinds of matter.
Method
Play this game in the field. Make four groups and form human chains.
(a) The first group should hold each other from the back and lock arms like Bihu dancers.
(b) The second group should hold hands to form a human chain.
(c) The third group should form a chain by touching each other with only their fingertips.
(d) Now, the fourth group of students should run around and try to break the three human chains one by one into as many small groups as possible.
Now answer
a. Which group was the easiest to break Why?
b. If we consider each student as a particle of matter, then in which group the particles held each other with the maximum force?
Answers
a. Third group, because they were weakly bonded with each other.
b. Ist group
If particles are bonded tightly, it is difficult to separate them.
Conclusion
Particles of matter attract each other.
(i) String increases the rate of interaction. Stirring helps to increase the interaction between sugar molecules and water molecules. Which causes sugar molecules to break away from each other. Hence they get dissolved faster.
(ii) Naphthalene balls disappear with time without leaving any solid because of they undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily.
(iii) when the temperature increases, the ice starts changing into water. This change is called "Melting". The temperature remains same till all the ice changes into water. The thermometer shows 0∘C until all the ice has melted.
(i) Since the interparticle spaces are the maximum in the gaseous state, the attractive forces are the least. As a result, the fluidity is very large while rigidity is negligible.
(ii) As compared to solids, liquids are generally light. This is on account of greater number of interparticle spaces in the liquid state as compared to the solid state of the same substance.
(iii) Natural gas is used extensively in the compressed from in vehicles. This form of natural gas is called compressed natural gas (CNG).
(iv) LPG (Liquified petroleum gas) and oxygen gas are the two gases that are supplied in compressed form in houses and hospitals.
Gases are compressible because on applying pressure, the spaces between the gaseous particles decreases. Therefore, gases can be compressed readily.
By applying pressure particles of gas can be brought close together.
(ii) Particles of matter have space between them when sugar is dissolved in water, the volume of the liquid remains unchanged because during dissolution, the particles of sugar get into the spaces between the particles of water.
Matter have spaces between the particles
As a result, they get evenly distributed and there is no noticeable change in volume. Similarly, when potassium permanganate is dissolved in water, its particles, get evenly distributed throughout the bulk of water. This is indicated by uniform colour of the solution.
This indicates that there are spaces between particles of matter. The particles of potassium permanganate get uniformly distributed in the spaces between water molecules.
Similarly, when we prepare tea, coffee or lemonade (nimbu pani) we observe that particles of one type of matter get into the spaces between particles of other.
Sublimation is the process by which a solid directly changes into a gaseous state on heating, without getting into the liquid state and vice versa upon cooling.
E.g. Ammonium chloride/Camphor changes into vapour upon heating.
Aim
To demonstrate the process of sublimation
Method
(a) Take some camphor or ammonium chloride.
(b) Powder it and put in a China dish.
(c) Place an inverted funnel over the China dish.
(d) Put a cotton plug on the stem of the funnel.
(e) Heat the China dish slowly.
Observation
We observe that solid camphor on heating gets converted into vapour which gets condensed on the funnel.
Solid state is directly converted into gaseous state. This experiment shows sublimation process.
More examples of sublimation
(i) In very cold places, the snow does not melt but sublimes directly to vapours.
(ii) In frost-free refrigerators, ice on the walls of the freezer sublimes when warm air is circulated through the compartment during the defrost cycle.
(Session 2025 - 26)