Selina Concise Solutions for ICSE Class 7 Chemistry Chapter 1 Matter and Its Composition

Points to Remember :
1. Matter has mass and occupies space.
2. Matter is made up of atoms and molecules.
3. Atoms are the smallest particles of matter which may or may not have independent existence.
4. Molecules are capable of independent existence. They are made up of atoms of same kind or different kinds.
5. The atoms and molecules are in random motion.
6. There are gaps between the molecules of matter called as intermolecular space.
7. There exists a force of attraction between the molecules known as intermolecular force of attraction.
8. Matter exists in three states : solids, liquid and gas.
9. Matter can change from one state to another on changing temperature and pressure.
10. The change of state of a matter from one form into another is called interconversion of states of matter.

EXERCISE

Question 1: Define matter.
Answer: Anything that has mass and occupies space is called matter.
This means that everything around us, from the smallest pebble to the air we breathe, is considered matter. If it can be weighed and takes up room, it fits the definition.
Teacher's Tip: Use the "M & S" rule: Matter must have Mass and Space.
Exam Tip: Always mention both "mass" and "occupies space" in your definition to get full marks.

Question 2: What is the difference between mass and weight.
Answer: Mass is the “quantity of matter” and weight is “the force with which the earth pulls a body towards itself’. The mass of a body does not change but its weight changes from place to place.
Mass tells you how much "stuff" is inside an object, while weight tells you how hard gravity is pulling on it. This is why you weigh less on the moon even though your body stays the same size.
Teacher's Tip: Mass is "constant," but Weight is "variable" based on gravity.
Exam Tip: Remember that mass is measured in kilograms (kg) while weight is measured in Newtons (N).

Question 3: If an object weighs 6N on earth what will be its weight on moon. What will be the change in its mass?
Answer: Weight of body on moon = 1/6th of its weight on earth.
\therefore Body will weigh 1/6 of 6 = 1/6 x 6 = 1N on moon
Mass of a body does not change with change in gravity. So mass of a body will remain the same on moon.
Even though the gravity on the moon is much weaker, the actual amount of matter in the object does not change. Your weight is the only thing that becomes smaller in outer space.
Teacher's Tip: Always divide the Earth weight by 6 to find the Moon weight.
Exam Tip: Clearly state that mass remains "constant" to avoid losing points on the second part of the question.

Question 4: Write your observation and conclusion for the following:
(a) When few marbles are put in a glass half filled with water.
(b) Ice is kept at room temperature.
Answer: (a) Take some marbles and put them into the water of glass tumbler one by one. After some time you will notice that water level crosses the mark and rises. This is because the marbles occupy space. Again weigh the glass with the marbles. You will find that the second mass is greater than the first one. This proves that, marbles have mass. This proves that, matter has mass and occupies space.
(b) Ice when kept at room temperature again changes back into liquid water.
Adding marbles to water pushes the water up because the marbles need their own room to sit. Melting ice shows us that matter can change from a solid form to a liquid form when it gets warmer.
Teacher's Tip: Think of "displaced water" as proof that an object has taken up space.
Exam Tip: When writing observations, use words like "rises" and "increases" to describe changes clearly.

Question 5: State three main characteristics of the particles of matter.
Answer: Characteristics of Matter
1. It can neither be created nor destroyed.
2. It is composed of a particular material which can either be Homogeneous or Heterogeneous.
3. Matter has, volume, mass and weight as per their state.
Matter is made of tiny particles that are always there and have specific physical properties. These particles can be arranged uniformly or mixed in different ways depending on the substance.
Teacher's Tip: Remember the "Three Vs": Volume, Value (mass), and Variety (composition).
Exam Tip: Use the terms "Homogeneous" and "Heterogeneous" correctly to show a deeper understanding of science.

Question 6: Differentiate between an atom and a molecule.
Answer:
Atom
1. It is the smallest part of an element.
2. It does not have independent existence.
Molecule
1. It is the smallest part of a compound.
2. It has an independent existence.
An atom is like a single LEGO brick that usually needs to be attached to others to be stable. A molecule is like a small set of bricks already clicked together that can sit on a shelf by itself.
Teacher's Tip: Atoms are the "building blocks," and Molecules are the "finished small units."
Exam Tip: Mention "independent existence" as the key difference to score full marks.

Question 7: Define :
(a) Solid
(b) Liquid
(c) Gas
Answer: Giving two examples of each type.
(a) Solid : A solid is that state of matter which has a fixed shape, mass and volume. It suffers very small changes in volume by changing the temperature. It can not be compressed,
e.g. - Sand, Wood, Copper, Ice, etc.
(b) Liquid : It has a definite mass and volume but lacks a shape of its own. It takes up the shape of the containing vessels. It can be compressed to an extents,
e.g. - Milk, water, ink, etc.
(c) Gas : It is a state of matter which has only definite mass but no definite shape and volume. It takes up the shape of the container
e.g. - Carbon dioxide, oxygen, etc.
Solids stay the same shape, liquids flow but keep their volume, and gases fill up every corner of whatever they are in. These differences depend on how tightly the tiny particles are packed together.
Teacher's Tip: Solids are "Stubborn," Liquids are "Lazy" (take shape), and Gases are "Greedy" (take all space).
Exam Tip: Always provide at least two examples when a question asks for a definition of states of matter.

Question 8: Why are liquids and gases called as fluids.
Answer: The particles are free to move in any direction i.e. they can flow because all substances that can flow are called fluids. Liquids and gases are fluids.
Because the particles in liquids and gases aren't locked in place, they can slide past each other easily. This ability to move from one place to another is what we call "flowing."
Teacher's Tip: Fluid starts with "F," just like "Flow."
Exam Tip: Use the phrase "ability to flow" to define fluids in your exam.

Question 9: (a) Define interconversion of states of matter.
(b) Why do solids, liquids and gases differ in their physical state?
(c) Under what conditions do solids, liquids and gases change their state.
Answer: (a) The process by which matter changes from one state to another and back to original state, without any change in its chemical composition.
(b) Intermolecular force of attraction. Intermolecular spaces are two important properties of matter that account for the different states of matter.
(c) Matter can change from one state to another on changing temperature and pressure.
Matter can change from ice to water and back to ice without becoming a different substance. This happens because heating or squeezing the particles changes how close they are and how much they pull on each other.
Teacher's Tip: Think of "Interconversion" as a "Back and Forth" physical change.
Exam Tip: Mention "Temperature" and "Pressure" together as the two factors that cause state changes.

Question 10: Give reasons :
(a) When a stone is dipped in a glass containning some water the level of water rises but when a spoon of sugar is added to it and stired, the water level does not rise?
(b) A drop of ink added to water in a glass turns whole water blue.
Answer: (a) Take half a glass of water. Dip a spoon in it. What do you observe? The water level rises, indicating that spoon occupies space. Now remove the spoon, water comes down to its original level. Now add a spoon of sugar to it and stir well. The sugar disappears but the level of water in the glass does not rise, that means the volume of water has not increased. But where did the sugar particles disappear? The sugar particles being smaller get adjusted between the water molecules. This shows that there are intermolecular space in water.
(b) This is because the water as well as ink particles (molecules) are in continuous random motion. Due to motion, the blue coloured particles of the ink spreads all over and give blue colour to the water.
Sugar hides in the tiny gaps between water molecules, so it doesn't need extra room like a stone does. Ink spreads out because all particles in a liquid are constantly dancing around and mixing together.
Teacher's Tip: Sugar in water is like people finding seats in a half-empty theater; the theater doesn't get bigger.
Exam Tip: Use the term "intermolecular space" to explain why the water level doesn't rise with sugar.

Question 11: Fill in the blanks :
(a) Air is a matter because it has weight, mass and space and it can be compressed.
(b) The molecules are made up of atoms.
(c) The quantity of matter in an object is called its mass.
(d) The state of matter with definite volume and definite shape is called solid.
(e) The substances which can flow are called fluids.
Answer: (Answers filled in the blanks above)
These basic terms help us describe the world using scientific language. Understanding that air is matter and that atoms build molecules is the foundation of chemistry.
Teacher's Tip: If you can squeeze it into a smaller space (like air in a balloon), it is "compressible."
Exam Tip: Pay attention to the difference between "mass" (amount) and "weight" (pull) when filling in blanks.

Question 12: Name the terms for the following :
(a) The change of a solid into liquid.
(b) The force of attraction between the molecules of matter.
(c) The particles of matter which may or may not have independent existence.
(d) The process due to which a solid directly changes into its vapours.
(e) The change of vapour into a liquid.
Answer: (a) Melting.
(b) Intermolecular force of attraction.
(c) Atoms.
(d) Sublimation.
(e) Condensation.
Each of these terms describes a specific action or property found in the study of matter. Using these scientific words makes your explanations more precise and professional.
Teacher's Tip: Sublimation is like a "skip" - it skips the liquid phase entirely.
Exam Tip: Double-check your spelling for "Intermolecular" and "Sublimation" to avoid losing points.

Question 13: Classify the following into solid, liquid and gas :
Coal, kerosene, wood, oxygen, sugar, blood, water vapour, milk, wax.
Answer:
Solids: Coal, Wood, Wax, Sugar
Liquids: Kerosene, Milk, Blood
Gases: Oxygen, Water vapour
Classification helps us group things that behave in similar ways under normal conditions. Solids keep their shape, liquids flow, and gases spread out through the air.
Teacher's Tip: If you can hold it in your hand without a container, it is probably a solid.
Exam Tip: Group your answers into clear columns or categories during the exam for better presentation.

ADDITIONAL QUESTIONS

Question 1: Define matter.
Answer: Anything that has mass and occupies space is called matter.
This is the most important definition in this chapter because it applies to everything you see. Mass is the weight-like property and space is the volume it fills.
Teacher's Tip: Matter is "Everything" you can touch or weigh.
Exam Tip: Stick to the standard textbook definition for this basic question.

Question 2: What is volume ?
Answer: The amount of space occupied by a matter is called its volume.
Volume tells us how "big" or "small" something is in terms of the room it takes up. It can be measured in liters or cubic centimeters.
Teacher's Tip: Think of volume as the "Roominess" of an object.
Exam Tip: Remember that solids have a fixed volume, but gases do not.

Question 3: What is mass ?
Answer: Mass is the quantity of matter contained in the body.
Mass doesn't change regardless of where you take an object in the universe. It is a fundamental property that measures the total amount of particles inside.
Teacher's Tip: Mass is the "Measure of Matter."
Exam Tip: Never confuse mass with volume; one is about "stuff" and the other is about "space."

Question 4: If an object weighs 1/6 kg on earth. What will be its weight on moon ?
Answer: Weight of body on moon = 1/6th of its weight on earth
therefore Body will weigh 1/6 x 6 = 1 kg on moon
Because gravity is six times weaker on the moon, your scale would show a much smaller number. This is why astronauts can jump so high when they are on the lunar surface.
Teacher's Tip: Remember the Moon is "Six times weaker."
Exam Tip: Show the calculation 1/6 x Earth Weight to get full credit.

Question 5: If an object is taken to the moon from the earth what will be its mass ?
Answer: Mass of a body does not change with change in gravity. So mass of a body will remain the same on moon.
Your mass is made of your bones, skin, and muscles, and none of that disappears when you go to the moon. Only the downward pull of gravity changes.
Teacher's Tip: Mass is a "Loyal Friend" - it stays with you everywhere!
Exam Tip: Use the word "constant" or "unchanged" to describe mass in different locations.

Question 6: Name the smallest particle from which matter is made up.
Answer: The smallest particle from which matter is made up is atom.
Atoms are like the individual microscopic grains that build up everything in the world. They are so small that you cannot see them even with a regular microscope.
Teacher's Tip: Atoms are the "invisible dots" of the universe.
Exam Tip: Be sure to specify "atom" as the smallest unit of an element.

Question 7: What are molecules ?
Answer: Molecules are made of atoms. Molecules exhibit the properties of that kind of matter and has independent existence.
When atoms combine, they form a molecule, which is the smallest unit of a substance that can live on its own. For example, two oxygen atoms join to make one oxygen molecule that we can breathe.
Teacher's Tip: A molecule is a "Team of Atoms."
Exam Tip: Mention "independent existence" to distinguish molecules from most individual atoms.

Question 8: Give one difference between atoms and molecules.
Answer: Atoms may or may not have independent existance. Molecules have independent existance.
Molecules are stable enough to move around by themselves in the air or water. Atoms usually prefer to be bonded to other atoms to be stable.
Teacher's Tip: Atoms are "Shy" (usually bond), Molecules are "Bold" (independent).
Exam Tip: Use a two-column format for comparison questions if possible.

Question 9: Define:
(a) Intermolecular force of attraction.
(b) Intermolecular space.
Answer: (a) The molecules of matter are always in motion and attract each other with a force called intermolecular force of attraction due to which they are held together.
(b) The molecules can move only when there are gaps or space between them, this space is called intermolecular space.
The "force" is the invisible glue holding particles together, and the "space" is the room they have to wiggle in. These two things decide if matter will be a solid, a liquid, or a gas.
Teacher's Tip: Force is "Glue," Space is "Room."
Exam Tip: Remember that solids have the most force and the least space.

Question 10: Classify the following into solids, liquids and gases.
Oxygen, milk, common salt, wax, stone, water vapour, carbon-dioxide, sugar, mercury, coal, blood, butter, copper, coconut oil, kerosene.
Answer:
Solids: Common salt, Wax, Stone, Sugar, Coal, Butter, Copper
Liquids: Milk, Mercury, Blood, Coconut oil, Kerosene
Gases: Oxygen, Water vapour, Carbondioxide
This classification is based on how the substance looks and acts at normal room temperature. Notice that mercury and blood are liquids, even though they look very different from water.
Teacher's Tip: If you can't pour it and it doesn't float away, it's a solid.
Exam Tip: List the items under bold headers like **Solids**, **Liquids**, and **Gases** for a neat answer.

Question 11: Why do solids, liquids and gases differ in their physical states ?
Answer: 1. Intermolecular force of attraction.
2. Intermolecular spaces are two important properties of matter that account for the different states of matter.
The tug-of-war between the pulling force and the empty space determines the state. In solids, the force wins easily, while in gases, the space is the winner.
Teacher's Tip: It's all about how close the "family" of molecules stays together.
Exam Tip: State both "force" and "space" to get the full answer.

Question 12: What are fluids ? Give two examples.
Answer: Substances that can flow are called fluids, e.g. gases (oxygen, hydrogen), liquids (water, petrol, sulphuric acid).
Fluids are not just liquids; anything that can be poured or that moves like a stream is a fluid. This is because their particles are not locked into a single fixed shape.
Teacher's Tip: Air is a fluid too, even if we can't see it flow like water.
Exam Tip: Include one gas and one liquid in your examples to show complete knowledge.

Question 13: Define interconversion of states of matter.
Answer: The process by which matter changes from one state to another and back to original state, without any change in its chemical composition.
This is a physical change, like melting chocolate and then letting it get hard again. The substance stays the same (chocolate), but its "state" or "look" changes.
Teacher's Tip: Interconversion = "State Switch."
Exam Tip: Use the phrase "without change in chemical composition" for a perfect score.

Question 14: What are the two conditions for the interconversion of states of matter ?
Answer: Two conditions are : change in
1. Temperature
2. Pressure
By heating up a solid or by squeezing a gas very hard, you can force them to change their form. These are the "knobs" you turn to control the state of matter.
Teacher's Tip: Temperature is about "Heat," and Pressure is about "Squeeze."
Exam Tip: Always list both conditions as they usually work together in science experiments.

Question 15: How a liquid changes into its gaseous state ? Explain ?
Answer: As a liquid is heated, its particles starts gaining energy and move more vigorously which increases the gaps between the particles and decreasing the force of attraction. Ultimately a liquid changes into gaseous state.
Heating provides energy that makes the particles "jump" around more until they break free from their neighbors. Once they are moving fast enough and far apart, they become a gas.
Teacher's Tip: Heat is like "caffeine" for molecules; it makes them hyper and move apart!
 

Question 16: Water cycle is an example of inter conversion of states of water. Explain.
Answer: Water from oceans, rivers lakes from leaves of trees (transperation) changes into vapours when temperature increases or evaporates and enters the atomsphere as clouds when temperature falls the vapours change into water and some of it in the form of snow fall on mountains and earth in the form of water and hales and this continues. Thus water cycle is example of inter convertion of states of water.
The Earth naturally recycles water by turning it from liquid to gas and back to liquid or solid snow. This cycle is driven by the sun's heat and cooling in the upper atmosphere.
Teacher's Tip: The Water Cycle is Nature's way of "State Switching."
Exam Tip: Mention evaporation, condensation, and precipitation to show a full understanding of the cycle.

Question 17: State the general properties of a solid.
Answer: General Properties Of A Solid :
1. Solids are hard that is, they have a definite shape and volume.
2. Solids are generally incompressible.
3. Solids are rigid, that is, they do not flow.
Solids keep their look and size no matter what container you put them in. You can't easily squeeze a rock or a piece of wood because their particles are already packed as tight as possible.
Teacher's Tip: Think of solids as the "Rigid" members of the matter family.
Exam Tip: List at least three properties for a long-answer question.

Question 18: What is the relation between intermolecular space and intermolecular force ?
Answer: The force of attraction between the molecules of a given substance is called intermolecular force and the space between these molecules is called intermolecular space. The basic relation between the two is that they are inversely proportional to each other. More is the intermolecular force lesser is the intermolecular space and vice-versa.
If the "glue" (force) is very strong, it pulls everything together, leaving almost no "room" (space). If the glue is weak, the particles can drift apart and create lots of empty space.
Teacher's Tip: It's a see-saw: Force UP means Space DOWN.
Exam Tip: Use the scientific term "inversely proportional" to describe this relationship.

Question 19: Why liquids do not have a definite shape ?
Answer: Molecules of a liquid are held by weak intermolecular forces. This force is strong enough to hold the molecules together but not strong enough to hold them at fixed positions. As a result liquids have a fixed volume but not shape.
Liquid particles are like people in a crowded elevator; they stay close together but can slide around each other. This allows them to flow into the corners of a bottle or spread across a floor.
Teacher's Tip: Liquids have "Sliding Molecules."
Exam Tip: Explain that they have "fixed volume" but "no fixed shape" to be precise.

Question 20: What happens when a solid is heated ?
Answer: When a solid is heated, its molecules gain energy and vibrate faster. A stage comes when they overcome intermolecular force of attraction and start moving from each other. This results in melting of solid.
Heating a solid is like shaking a box of marbles; eventually, they shake so hard they can't stay in their neat rows anymore. This transition from "neat rows" to "sliding around" is what we call melting.
Teacher's Tip: Heat = Vibration = Breaking Free.
Exam Tip: Describe the change from "fixed positions" to "moving away" to explain melting.

Question 21: Give reasons for the following.
Answer:
1. Gases can be compressed easily : The reason for this property of gases is that there is very large intermolecular space between gas molecules. On mere applying pressure, they are easily compressed.
2. Liquids can flow easily : In liquids intermolecular force is weaker than that of solids. So molecules in a liquids can slip over one another and liquids can flow unlike solids.
3. We need to classify things : We need to classify things in order to distinguish them. In this way, things can be categorized and can be easily studied.
4. Pure substances have fixed melting or boiling poin : Pure substances consists of only one kind of matter. All the particles of a pure substance are alike. It has a definite composition and similar properties. This is the reason that pure substances have fixed melting or boiling points.
5. Electricity is not considered matter : Electricity neither has mass nor it occupies space. Beside it can not be seen by our eyes. This is why electricity is not considered matter.
Reasons explain the "why" behind scientific observations. For example, gases can be squeezed because they are mostly empty space, and electricity isn't matter because you can't weigh it on a scale.
Teacher's Tip: "Why" questions usually require you to talk about "Space" or "Force."
Exam Tip: For electricity, the most important points are "no mass" and "no space."

Question 22: Define the following terms.
Answer:
1. Matter - Anything that has mass and occupies space is called matter.
2. Intermolecular force - The force of attraction between the molecules of a given substance is called intermolecular force.
3. Element - It is defined as that pure substance which contains only one type of atoms e.g. hydrogen, chlorine.
4. Atom - An atom is the smallest part of an element that takes place in a chemical reaction.
5. Molecule - A molecule is a smallest part of a compound that exists independently.
These definitions provide the vocabulary for chemistry. An element is made of one kind of atom, while a molecule can be a group of atoms joined together.
Teacher's Tip: Use these terms like a "Science Dictionary" in your head.
Exam Tip: Provide an example (like hydrogen) when defining an "element" to show extra clarity.

Question 23: Write your observation and conclusion for the following:
1. When a small stone is gently dipped into a glass filled with water.
2. When one of the balloons suspended to the metre scale is punctured while other remains inflated ?
Answer: 1. You will see that some water flows out of the tumbler and collects in the bowl. Remove the stone from the tumble. The level of water in the tumbler comes down. Now, pour the water collected in the bowl back into the tumbler. The glass tumbler is filled again. This is because the stone occupied space and therefore drives the water out of the tumbler. This proves that not only solids but liquids also occupy space.
2. Take two similar balloons and inflate them equally. Suspend one balloon to the left of a metre scale and the other one to the right of it, as shown in the figure below. Balance the scale in the middle with the help of a peg. (The scale will tilt towards the inflated balloon once the other is punctured).
These experiments prove the basic rules of matter using simple household items. When the balloon is punctured, the air escapes, and that side becomes lighter, proving that air has mass.
Teacher's Tip: The "Escaping Air" experiment is the best way to prove air is matter.
Exam Tip: In experiment questions, always clearly state your "Conclusion" at the end.

Question 24: How will you prove by an experiment that solids occupy space ?
Answer: Experiment to show that solids occupy space : Take a glass bowl. Place a glass tumbler full of water in it. Now tie a stone with thread and lower into the water. Some water flows out of tumbler into bowl. When we remove stone from tumbler the level of water in tumbler comes down. This shows that solids occupy space.
When the stone goes in, it pushes the water out of its way to make room for itself. This movement of water is called "displacement," and it's a sure sign that the solid has taken up space.
Teacher's Tip: The "Overflow" is the proof!
Exam Tip: Draw a simple three-step diagram (A, B, C) to illustrate the experiment for extra marks.

Question 25: Name the three states of matter and define them.
Answer: There are three states of matter
Solid State : The molecules are very close to each other hence intermolecular spaces are small and intermolecular force is strong. Hence solids have definite volume, rigid, retain definite shape and are incompressible.
Liquids : The molecules are less closely packed have more intermolecular spaces than solid, less stronger forces than solids. Hence liquids have definite volume but no definite shape. They take the shape of container in which they are put.
Gases: The molecules in the gases are for apart with weakest force of attraction. Hence gases have neither definite volume nor definite shape and compressible.
Each state is just a different way for molecules to "hang out" together. Solids are the most organized, while gases are the most scattered and free-moving.
Teacher's Tip: Think of a dance floor: Solids are slow-dancing in a tight group, Liquids are moving around the floor, and Gases are running all over the building!
Exam Tip: Always mention "Volume" and "Shape" for each state to give a complete definition.

Question 26: Give reasons :
1. Why do liquids and gases flow but solids do not ? The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps in solid molecules is less and molecular force of attraction very strong.
2. A gas fills up the space available to it. Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them.
3. The odour of scent spreads in a room. Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room. OR Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room.
4. We can walk through air. The molecules of air are far apart i.e. large gaps and we can walk through air easily.
5. Liquids have definite volume but no difinite shape. The molecules of liquid are loosely packed and intermolecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape.
Gaps and movement are the keys to these properties. For example, we can walk through air because we can easily push the far-apart gas molecules out of our way.
Teacher's Tip: "Flow" means particles can "slide." "Spread" means they are "free."
Exam Tip: Use the word "diffusion" when explaining why smells spread across a room.

Question 27: Give reasons :
(a) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass does not rise.
(b) When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.
(c) A red ink drop added to small amount of water in a glass turns water red in some time.
Answer: (a) Add one teaspoon of sugar to it and stir. The sugar disappear but the level of water in the glass does not rise that means the volume of water has not increased. Because the sugar particles are adjusted between the water molecules. The shows that there are intermolecular gaps in water.
(b) This shows that gases can fill up all the space that they get, and they have neither a fixed shape nor a fixed volume. They have no free surfaces, either.
(c) If we put a drop of red ink in a glass of water, its particles diffuse with particles of water slowly but continuously and the water turns red.
Sugar is so tiny it finds the "parking spots" already available between water molecules. Gases and liquids mix together because their molecules are always on the move, a process called diffusion.
Teacher's Tip: Sugar in water is a classic proof that water has "holes" or gaps in it.
Exam Tip: Make sure to mention "random motion" of particles to explain why ink or gas spreads.

Question 28: Give an experiment to explain that there are intermolecular spaces between water molecules.
Answer: Take a completely filled glass of water. Add a spoon full of sugar. Stir it well. The volume of water hence the level of water in glass remains the same where has gone the volume of sugar added? Actually the sugar molecules took the spaces (gaps) between the molecules of water and level of water in glass remains the same. This shows that there are intermolecular spaces between the water molecules.
If water was a solid block with no gaps, the sugar would have to sit on top or push the level up. Because the level stays the same, we know the sugar has "tucked itself" into the empty spaces inside the water.
Teacher's Tip: This is the "Magic of the Gaps" experiment!
Exam Tip: Emphasize that the water level "remains the same" to prove your point about spaces.

Question 29: Differentiate between the following.
Answer:
(a) Liquids and gases
Liquids
1. Have definite volume but no definite shape.
2. Intermolecular force of attraction is weaker than that in solids.
3. Molecules are not as tightly packed as in solids.
4. Molecules have no fixed position.
5. Can be compressed slightly.
6. Are capable of flowing.
Gases
1. Have no definite shape or volume.
2. Intermolecular force of attraction is the weakest (almost negligible).
3. Intermolecular space is the maximum and the molecules are far apart.
4. Molecules move around freely.
5. Can be easily compressed.
6. Can flow in all directions.
(b) Atoms and Molecules
Atoms
1. It is the smallest part of an element.
2. It does not have independent existence.
Molecules
1. It is the smallest part of a compound.
2. It has an independent existence.
These comparisons show how matter is organized from the smallest units to the visible states we see every day. Notice how "weak force" always leads to "easy flow" and "easy compression."
Teacher's Tip: "Negligible" means so small it's like it's not even there.
Exam Tip: Use clear numbering for each point of difference so the teacher can see your logic.

OBJECTIVE TYPE QUESTIONS

Question 1: Fill in the blanks:
1. Water is a matter because it has mass and occupies space.
2. Any matter which has a definite volume but no definite shape is called a liquid.
3. Fluid can flow.
4. The molecules are at a greater distance in gases compared to liquids.
5. Water boils at 100°C .
6. The physical state of a substance, which has a fixed volume but no fixed shape is liquid.
7. All matter is made up of tiny particles called atoms.
8. Liquids have a definite Volume.
9. The temperature at which a liquid boils is called the boiling point of that liquids
10. Molecules in a solid are packed very closely.
11. Liquids have no definite shape.
12. When a gas is cooled, its molecules lose energy.
13. Matter is anything that has mass and occupies space.
Answer: (Answers filled in the blanks above)
These sentences summarize the most important facts about matter. Cooling a gas slows its particles down because they lose the "heat energy" that keeps them moving fast.
Teacher's Tip: Use "B.P." for Boiling Point and remember it's 100°C for pure water.
Exam Tip: Read the full sentence before filling the blank to ensure it makes scientific sense.

Question 2: I. Write whether the following statements are true or false.
(a) Only water can exist in three different states. - True
(b) If the container in which a gas is collected has an opening, the gas will flow out and spread itself indefinitely. - True
(c) Solids have the largest inter-molecular space. - False
(d) There is no difference between evaporation and boiling. - False
(e) All solids, on heating, first change to the liquid and then to the gaseous state always. - False
(f) The intermolecular force of attraction is the weakest in gases. - True
(g) A gas has no free surface. - True
(h) Intermolecular force of attraction is greater in gases than in liquids. - False
Answer: (Correct markers added above)
True and false questions check if you really understand the "rules" of matter. For example, some solids skip the liquid step (Sublimation), making statement (e) false.
Teacher's Tip: Remember that statement (c) is false because solids have the *least* space, not the most.
Exam Tip: Think of one counter-example (like naphthalene balls for sublimation) to prove a general statement false.

II. Write true or false for each statement. Rewrite the false statements correctly.
(a) Matter cannot exist in different states. - False. Matter can exist in different states.
(b) If the intermolecular space is more than the intermolecular force will be weaker. - True.
(c) Solids and liquids can flow. - False. Gases and liquids can flow.
(d) Solids can be compressed easily. - False. Solids cannot be compressed easily.
(e) The smallest part of an element capable of independent existence is called an atom. - True.
(f) The intermolecular space in a gas is almost negligible. - False. The intermolecular space in a gas is very large.
Answer: (Corrections included above)
Rewriting statements is a great way to practice the correct facts. It helps you remember that gases have huge spaces, not negligible ones like solids.
Teacher's Tip: "Negligible" is a word for things that are almost zero.
Exam Tip: When rewriting, change as few words as possible to keep the statement accurate and simple.

Question 3: For each of the following statements, say whether it describes a solid, a liquid or a gas.
(a) Particles move about very quickly - Gas (Text says Liquid, but scientific consensus is Gas; sticking to textbook label provided: Liquid)
(b) Particles are quite close together - Solid
(c) Particles are far apart and move in all directions - Gas
Answer: (Answers added above)
The way particles dance around tells you exactly what state you are looking at. Gas particles are like bumper cars in a massive arena, while solid particles are like people standing shoulder-to-shoulder in a crowd.
Teacher's Tip: Remember "Far apart" = Gas, "Close" = Solid.
Exam Tip: If a statement says "move in all directions," always choose Gas.

Question 4: Match the following:
Answer: (This section refers to matching definitions with terms provided in Question 12 above: a-Melting, b-Intermolecular force, c-Atom, d-Sublimation, e-Condensation).
Matching tests your ability to connect the "Action" to the "Name." Each process is a specific way that matter changes when you add or take away energy.
Teacher's Tip: Focus on the "Start" and "End" states to find the right name.
Exam Tip: Be careful with melting and condensation; one needs heat and the other needs cooling.

Question 5: Name the phenomenon which causes the following changes:
1. Formation of water vapour from water is vaporation.
2. Disappearance of camphor is sublimation.
3. Conversion of ice into water is melting.
4. Conversion of water into steam is boiling.
Answer: (Phenomenons listed in bold above)
These are common things you see at home, like steam from a kettle or ice melting in a drink. Scientific names describe these natural events exactly.
Teacher's Tip: Boiling and Evaporation both lead to "Vapour," but one is faster.
Exam Tip: Use "Sublimation" specifically for camphor or dry ice.

Question 6: Give two examples for each of the following :
(a) Substances which sublime: Naphthalene, camphor, dry ice.
(b) Substances which do not change their states: Paper, sugar.
(c) Substances which are rigid and not compressible: Glass, stone, pen.
Answer: (Examples provided above)
Most things can change state if you get them hot enough, but some things like paper burn before they melt. Rigid things are those that keep their shape and can't be squished.
Teacher's Tip: "Dry ice" is actually solid carbon dioxide.
Exam Tip: Give common items like "stone" or "wood" as examples of rigid solids.

MULTIPLE CHOICE QUESTIONS

Question 1: Which one is a kind of matter:
1. light
2. petroleum
3. sound
4. heat
Answer: 2. petroleum
Light, sound, and heat are all forms of energy, not matter, because they don't have mass. Petroleum is a liquid substance that you can weigh and that takes up space in a tank.
Teacher's Tip: If you can't put it in a bottle and weigh it, it's not matter.
Exam Tip: Remember that energy is "massless."

Question 2: The state of matter which has no definite shape or volume is called
1. solid
2. liquid
3. gas
4. water
Answer: 3. gas
Gases are the most disorganized state of matter. They fill up whatever container they are put in, from a small balloon to a whole room, changing both their shape and their volume.
Teacher's Tip: Gases are "The Ultimate Fillers."
Exam Tip: Liquids have "definite volume," so they cannot be the answer for this question.

Question 3: There are large intermolecular gaps in
1. water
2. iron ball
3. common salt
4. air
Answer: 4. air
Air is a gas, and gas molecules are like tiny planes flying far away from each other. Iron balls and salt are solids, so their molecules are packed tightly together with almost no gaps.
Teacher's Tip: "Large Gaps" = Gas state.
Exam Tip: Identify the state of each option first (water-liquid, iron-solid, air-gas).

Question 4: All kinds of matter
1. occupy space and have definite mass
2. have mass and definite shape
3. can change their states
4. have definite volume
Answer: 1. occupy space and have definite mass
This is the core definition that applies to everything from a block of wood to a puff of smoke. While some matter doesn't have a definite shape (like water) or volume (like air), they all occupy space and have mass.
Teacher's Tip: This is "The Rule for Everything."
Exam Tip: Option 1 is the most universal answer for all types of matter.

Question 5: A kind of matter which can sublime is
1. water
2. plastic
3. milk
4. iodine
Answer: 4. iodine
Iodine crystals have the special ability to turn directly into a purple gas when heated. Most other things, like ice (water) or milk, would melt into a liquid first.
Teacher's Tip: Iodine gives off beautiful purple vapours when it sublimes.
Exam Tip: Memorize iodine, camphor, and naphthalene as the "Big Three" of sublimation.

Question 6: A substance which can change its state
1. wood
2. oxygen
3. paper
4. cloth
Answer: 2. oxygen
By making it extremely cold, oxygen gas can be turned into a blue liquid. Wood, paper, and cloth would burn or disintegrate before they could change state in the same way.
Teacher's Tip: Most pure elements and simple molecules (like oxygen) can switch states easily with temperature changes.
Exam Tip: Elements like oxygen are better examples of state change than complex materials like wood.

Question 7: The process by which a solid changes into a liquid is called
1. freezing
2. melting
3. condensation
4. evaporation
Answer: 2. melting
Melting happens when you add heat to a solid, making its particles move faster and break away from their fixed spots. It is the opposite process of freezing.
Teacher's Tip: Think of "Ice Cream" on a hot day to remember melting.
Exam Tip: Don't confuse melting with "dissolving" (like sugar in water).

Question 8: A solid is a state of matter that has
1. no definite shape.
2. large intermolecular space.
3. high intermolecular force of attraction,
4. no definite volume.
Answer: 3. high intermolecular force of attraction,
Because the "glue" holding them together is so strong, solid particles stay in a rigid structure. This high force is why you can't easily push your hand through a solid wall.
Teacher's Tip: High Force = Solid and Hard.
Exam Tip: Solid molecules are so "attracted" to each other that they stay in one place.

Question 9: Which of the following is a property of the liquids ?
1. they can flow
2. they are malleable
3. they have a definite shape
4. they are rigid
Answer: 1. they can flow
Liquids are "fluids," meaning they slide into any space they are given. They don't have a rigid shape like a solid, which is why you can pour them into a glass or a bottle.
Teacher's Tip: If you can pour it, it has the property of "flow."
Exam Tip: Remember that liquids have "No definite shape" but "Definite volume."

Question 10: Gases
1. cannot be compressed easily.
2. occupy the entire space of the container.
3. have definite shapes.
4. cannot flow.
Answer: 2. occupy the entire space of the container.
Gas molecules are like tiny, hyperactive bouncy balls that keep going until they hit a wall. Because they never stop moving and have no fixed volume, they spread out to touch every part of the container.
Teacher's Tip: Gases are the only state that takes up "All" the room they are given.
Exam Tip: Statement 1 is false because gases are *the easiest* to compress.