Maharashtra Board Class 6 Science Chapter 5 Substances in the Surroundings heir States and Properties Solutions

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कक्षा 6 विज्ञान अध्याय 5 "Substances in the Surroundings – Their States and Properties" के शीर्षक को दर्शाता है। इसमें एक महिला शिक्षक को एक छड़ी के साथ खड़े दिखाया गया है, जो सीखने का प्रतीक है। हरे और नारंगी रंग की पृष्ठभूमि पर, अध्याय का नाम और विषय का उल्लेख है, जो छात्रों को आसपास के पदार्थों, उनकी अवस्थाओं और गुणों के बारे में पढ़ाए जाने वाले महत्वपूर्ण अवधारणाओं का संकेत देता है।

Substances In The Surroundings - Their States And Properties Class 6 Science Chapter 5 Questions And Answers Maharashtra Board

Questions And Answers

Std 6 Science Chapter 5 Substances In The Surroundings - Their States And Properties Question Answer Maharashtra Board

Class 6 Science Chapter 5 Substances In The Surroundings - Their States And Properties Question Answer Maharashtra Board

Question 1. In the paragraph below write 'solid', 'liquid' or 'gas' in each of the blank (brackets) depending on the substance referred to just before.
Question a. On a bright sunny day, Riya and Gargi are playing with a ball (.....) in the park. Gargi feels thirsty. So, Riya brings tender coconut water (.....) for her. At the same time, a strong breeze (.....) starts blowing and it also begins to rain (.....). They run back into the house (.....), change their clothes (.....) and then their mother gives them a cup (.....) of hot milk (.....) to drink.
Answer: solid, liquid, gas, liquid, solid, solid, solid, liquid.
In simple words: The states of matter (solid, liquid, gas) are applied to objects and substances described in the story based on their physical characteristics.

🎯 Exam Tip: Understanding the basic properties of solid, liquid, and gas is crucial for accurately identifying the state of various substances in everyday scenarios.

2. Discuss.

Question a. Riya pours some water from her bottle into another bottle. Does it change the shape of the water?
Answer: Yes, the shape of water changes as water is in liquid state. Liquids do not have a shape of its own. They take the shape of the container.
In simple words: Water, being a liquid, adapts its shape to fit any container it's poured into because liquids do not have a fixed shape.

🎯 Exam Tip: This question assesses knowledge of liquid properties, specifically their indefinite shape, which is a key characteristic for scoring.

Question b. Halima picks up a small stone from the ground and puts it in the water in a dish. Does the shape of the stone change?
Answer: No, the shape of the stone does not change. Stone is a solid, hence retains its shape.
In simple words: The stone's shape remains the same because it is a solid, and solids maintain their own definite shape regardless of the container.

🎯 Exam Tip: Correctly identifying the properties of solids, such as a definite shape, is vital for answering questions related to states of matter.

3. Write The Properties Of These Substances.

Question a. Write the properties of these substances. (water, glass, chalk, iron ball, sugar, salt, flour, coal, soil, pen, ink, soap)
Answer: Properties of substances:

Substance	State	Properties
1. Water	Liquid	Fluidity, density, solubility, transparency, thermal conductivity.
2. Glass	Solid	Brittleness, hardness, density, transparency.
3. Chalk	Solid	Brittleness, density.
4. Iron ball	Solid	Hardness, density, malleability, ductility, electrical ductility, conductivity, thermal conductivity, luster, sonority.
5. Sugar	Solid	Brittleness, density, solubility.
6. Salt	Solid	Brittleness, density, solubility.
7. Flour	Solid	Density, solubility.
8. Coal	Solid	Brittleness, density, thermal conductivity.
9. Soil	Solid	Brittleness, density.
10. Pen	Solid	Hardness, density.
11. Ink	Liquid	Fluidity, density, solubility.
12. Soap	Solid	Brittleness, hardness, density, solubility.

In simple words: This table lists various common substances, identifies their state of matter, and describes their specific physical properties like fluidity, hardness, solubility, and conductivity.

🎯 Exam Tip: For full marks, ensure all listed properties are accurate and specific to each substance, demonstrating a thorough understanding of material science concepts.

Question 4. What is sublimation? Write the names of everyday substances that sublimate.
Question a. What is sublimation? Write the names of everyday substances that sublimate.
Answer:
1. The change of a solid substance directly into a gas or vapour without first changing into liquid is called sublimation.
2. Substances that sublimate: Camphor, naphthalene balls, ammonium chloride, iodine.
In simple words: Sublimation is when a solid turns directly into a gas without becoming a liquid first, and common examples include camphor and naphthalene balls.

🎯 Exam Tip: Defining sublimation correctly and providing at least two common examples will ensure full credit for this question.

Question 5. What is made from? Why?
a. A sickle to cut sugarcane.
Question a. A sickle to cut sugarcane.
Answer: A sickle is made of iron. An iron sickle is hard and malleable. When sharpened it will be able to cut the hard sugarcane.
In simple words: A sickle is made of iron because iron is hard and can be sharpened to effectively cut sugarcane.

🎯 Exam Tip: When explaining "why," link the material's properties (e.g., hardness, malleability) directly to its function for a comprehensive answer.

Question b. The sheets used for roofing:
Answer:
1. The sheets used for roofing are made of plastic, aluminium.
2. Plastic is hard, hence, protects against weather conditions.
3. Plastic is transparent, hence, sunlight can pass through it.
4. Aluminium is hard, light weight and durable, hence, protects against all weather conditions.
5. Malleable hence formed into thin sheets.
In simple words: Roofing sheets are made from plastic or aluminum because these materials are hard, durable, and can be shaped into thin sheets to protect against weather, with plastic also allowing sunlight through.

🎯 Exam Tip: List multiple properties for each material and explain how each property contributes to the material's suitability for roofing.

Question c. A screwdriver:
Answer:
1. A screwdriver is made up of iron, steel, aluminium.
2. A screwdriver possesses property of hardness hence, it easily pierces a screw in piece of wood, wall, metals etc.
In simple words: Screwdrivers are made from iron, steel, or aluminum because their hardness allows them to effectively turn screws into various materials.

🎯 Exam Tip: Focus on the primary property, hardness, as the key reason for the material choice in a screwdriver.

Question d. A pair of tongs:
Answer:
1. A pair of tongs are made up of iron, steel aluminium etc. Tongs are used to lift hot, boiling utensils or vessels.
2. Tongs are hard, ductile and malleable.
3. Hence, have strong grip to hold utensils.
4. Rubbers fitted on the ends will protect from thermal conduction, from burns.
In simple words: Tongs are made from hard, ductile, and malleable metals like iron or steel to provide a strong grip for lifting hot objects, often with rubber tips for insulation and safety against burns.

🎯 Exam Tip: Emphasize both the material properties for grip and strength, and the additional safety feature of rubber ends for thermal insulation.

Question e. Electric cables:
Answer:
1. Electric cables are metal wires (thin) wound in plastic.
2. Metal wires possess the property of hardness, ductility, electrical conductivity.
3. Plastic /rubber covering possesses the property of hardness, elasticity and are bad conductors of heat and electricity.
In simple words: Electric cables use ductile metal wires for electrical conductivity and are covered with plastic or rubber for insulation due to their hardness, elasticity, and poor conductivity of heat and electricity.

🎯 Exam Tip: Clearly distinguish the roles and properties of both the metal core (conductivity) and the insulating covering (non-conductivity, protection) in electric cables.

Question f. Ornaments:
Answer:
1. They are made up of metals like gold and silver.
2. They possess the property of hardness, ductility, malleability, lustre.
In simple words: Ornaments are made from metals like gold and silver because these metals are hard, ductile, malleable, and possess a desirable shine.

🎯 Exam Tip: Highlight the aesthetic (lustre) and physical (hardness, malleability, ductility) properties that make gold and silver suitable for ornaments.

Question g. Pots and pans: Answer:
Answer:
1. They are used to cook food, hence metals like aluminium, steel are used.
2. They possess the property of hardness, ductility, malleability, thermal conductivity, electrical conductivity, (microwave ovens)
In simple words: Pots and pans are made from metals like aluminum and steel because their hardness, ductility, malleability, and high thermal conductivity make them ideal for cooking.

🎯 Exam Tip: Focus on thermal conductivity as the primary reason for using metals in cooking utensils, along with other structural properties.

Question 6. What will happen if ....? And why?
Question a. Nails are made of plastic
Answer: If nails are made of plastic, they will not be able to pierce through other substances on being pushed or forced by a hammer. Plastic lacks the property of hardness.
In simple words: Plastic nails would be useless because plastic isn't hard enough to pierce materials, unlike metal.

🎯 Exam Tip: Explain both the consequence (inability to pierce) and the underlying property (lack of hardness) for a complete answer.

Question b. A bell is made of wood.
Answer:
1. If a bell is made of wood it will never make a ringing sound. A wooden bell does not have the property of being sonorous.
2. Sonority is the property of metals to produce a ringing sound.
In simple words: A wooden bell wouldn't ring because wood isn't sonorous, meaning it doesn't produce the clear ringing sound that metals do.

🎯 Exam Tip: Define sonority and link its absence in wood to the inability to produce a ringing sound for a clear explanation.

Question c. Rubber is not fitted on a pair of tongs.
Answer:
1. Rubber is a bad conductor of heat and electricity. It will not allow heat to pass to the hands/handle of the tongs, thus protecting us.
2. Pair of tongs are made up of metals which conduct heat and electricity. They have file property of thermal conduction and electrical conduction.
3. If rubber is not fitted on a pair of tongs, we will not be able to lift hot objects with it.
In simple words: Without rubber grips, metal tongs would conduct heat, making it impossible to safely lift hot objects because rubber insulates against heat.

🎯 Exam Tip: Focus on rubber's insulating property (bad conductor of heat) and its importance for safety when handling hot objects with metal tongs.

Question d. A knife is made of wood.
Answer: Wood does not have the property of malleability. Therefore, the edge of wooden knife will be blunt. Hence, we will not be able to cut anything with it.
In simple words: A wooden knife would be blunt and useless for cutting because wood lacks malleability, meaning it cannot be sharpened to a fine, cutting edge.

🎯 Exam Tip: Emphasize malleability as the critical property for forming a sharp edge, which wood lacks, rendering it unsuitable for knives.

Question e. An axe is made of rubber.
Answer:
1. If an axe is made of rubber, it will not be used to cut wood or tree.
2. Rubber does not have the property of hardness that is required to push through to cut it.
In simple words: A rubber axe couldn't cut wood because rubber lacks the hardness needed to penetrate and cut through tough materials.

🎯 Exam Tip: Clearly state that hardness is the key property an axe needs, and rubber's lack of it makes it unsuitable for the task.

Question 7. Who am I?
Question a. I'm found in a thermometer, I measure your temperature.
Answer: Mercury
In simple words: I am Mercury, the liquid metal often used in thermometers to measure temperature.

🎯 Exam Tip: Recognizing mercury's common application in thermometers is key for this type of riddle question.

Question b. I make things hot or cold.
Answer: Heat
In simple words: I am heat, the energy that causes substances to become either hot or cold.

🎯 Exam Tip: This question tests basic understanding of heat as the agent for temperature changes; a direct and simple answer is best.

Question c. I have no shape whatsoever!
Answer: Liquid, gases
In simple words: Liquids and gases both lack a definite shape, instead taking the form of their container.

🎯 Exam Tip: Differentiating between substances with definite versus indefinite shapes is fundamental to understanding states of matter.

Question d. I dissolve in water, but not in kerosene.
Answer: Salt
In simple words: I am salt, which easily dissolves in water but not in kerosene due to differences in chemical properties.

🎯 Exam Tip: This question tests knowledge of solubility and "like dissolves like" principle (polar vs. non-polar solvents).

Question 8. Why does this happen?
Question a. Coconut oil thickens in winter.
Answer: Coconut oil is in liquid state. In winter the surrounding temperature / atmospheric temperature starts decreasing. Coconut oil starts cooling or losing heat, it changes to solid state. Thus coconut oil thickens in winter.
In simple words: Coconut oil thickens in winter because as the temperature drops, it loses heat and solidifies from its liquid state.

🎯 Exam Tip: Connect the change in state (liquid to solid) directly to the drop in temperature and loss of heat for a clear explanation.

Question b. Kerosene left open in a dish disappears.
Answer: When kerosene is left open in a dish, it is exposed to surrounding temperature. As the temperature is more, kerosene starts continuously evaporating and finally disappears.
In simple words: Kerosene disappears when left open because it evaporates into the air due to exposure to the surrounding temperature.

🎯 Exam Tip: The key concept here is evaporation, where a liquid changes to a gas at room temperature due to heat absorption from the surroundings.

Question c. The fragrance of incense sticks lighted in one corner of a room spreads to the other corner.
Answer: The fragrance of incense sticks is given out in the form of scented vapours. As vapours are in gaseous state, the gas molecules spread out in the room. The molecules of gas move very fast and there are no forces to stop them from going apart. Therefore the fragrance of incense sticks lighted in one corner of room spreads to the other corner.
In simple words: The smell of incense sticks spreads because the scented vapors released are gas molecules that move quickly and freely, diffusing throughout the entire room.

🎯 Exam Tip: Focus on the concept of diffusion of gas molecules and their rapid, free movement as the core explanation.

Question d. What you see in the picture.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र पानी से भरे एक कंटेनर को दर्शाता है, जिसमें एक पीली प्लास्टिक की गेंद पानी की सतह पर तैर रही है और एक लाल सेब कंटेनर के तल पर डूब गया है। यह घनत्व के सिद्धांत को प्रदर्शित करता है, जहाँ कम घनत्व वाली वस्तु (प्लास्टिक की गेंद) तैरती है और अधिक घनत्व वाली वस्तु (सेब) डूब जाती है।
Answer: The mass of plastic ball is less than an apple. This difference is because of their densities. Since an apple has greater density, it will sink to the bottom on other hand the plastic ball has lesser density, it will float over water surface.
In simple words: The plastic ball floats and the apple sinks due to differences in their densities; the plastic ball has lower density than water, while the apple has a higher density.

🎯 Exam Tip: Clearly state the relationship between density and buoyancy; objects less dense than water float, while those more dense sink.

Activity:

Question 1. Find out how the big statues of wax are made.
Answer: [No answer provided in the original text, providing a generic placeholder]
In simple words: Large wax statues are typically made by melting wax, pouring it into molds, and then carving or refining the cooled wax.

🎯 Exam Tip: For activity-based questions, describe the main steps involved in the process clearly.

Question 2. Visit a jeweller's shop and find out how ornaments are made.
Answer: [No answer provided in the original text, providing a generic placeholder]
In simple words: Jewelers make ornaments by melting precious metals, shaping them through casting or hammering, and then polishing or setting stones.

🎯 Exam Tip: When detailing a process, include key techniques like melting, shaping (casting/hammering), and finishing steps.

Class 6 Science Chapter 5 Substances In The Surroundings - Their States And Properties Important Questions And Answers

Fill In The Blanks:

Question 1. The state of a substance changes if it is ............... or ............... .
Answer: heated, cooled
In simple words: A substance changes its state, like from solid to liquid, when it is either heated or cooled.

🎯 Exam Tip: Remember that heat addition or removal are the primary drivers for changes in the physical state of matter.

Question 2. Every substance in our surroundings is found in either the ............... or gaseous state.
Answer: solid, liquid
In simple words: All substances around us exist in one of three states: solid, liquid, or gas.

🎯 Exam Tip: Listing the three fundamental states of matter is essential for questions about general substance forms.

Question 3. On ............... heat, the substance changes from solid to liquid and liquid to gas.
Answer: gaining
In simple words: A substance changes from solid to liquid and then to gas when it gains heat.

🎯 Exam Tip: Associate gaining heat with phase transitions that move towards higher energy states (solid to liquid, liquid to gas).

Question 4. When the substance cools, or ............... heat, it changes from gaseous to liquid and liquid to solid state.
Answer: loses
In simple words: When a substance cools down, meaning it loses heat, it transitions from gas to liquid and then from liquid to solid.

🎯 Exam Tip: Connect losing heat with phase transitions that move towards lower energy states (gas to liquid, liquid to solid).

Question 5. A ............... amount of heat must be gained or lost before the state of a substance can change.
Answer: specific
In simple words: A substance needs to gain or lose a specific amount of heat to change its state.

🎯 Exam Tip: The term "specific" highlights that each substance has unique energy requirements for phase changes.

Question 6. When a substance gets heat, it becomes ........... and then ........... .
Answer: warm, hot
In simple words: When a substance absorbs heat, its temperature rises, making it feel warm and then hot.

🎯 Exam Tip: This question covers the basic observation of temperature increase when heat is applied to a substance.

Question 7. If the substance is very hot, we could get ............... .
Answer: scalded
In simple words: Touching a very hot substance can cause a burn known as a scald.

🎯 Exam Tip: Use correct terminology for injuries associated with heat for precision in answers.

Question 8. A thermometer is used to measure ............... .
Answer: temperature
In simple words: A thermometer is a tool specifically designed to measure temperature.

🎯 Exam Tip: Know the function of common scientific instruments, like a thermometer, for measuring physical quantities.

Question 9. ............... is the unit of measuring temperature.
Answer: Degree Celsius (°C)
In simple words: Degree Celsius is the standard unit used to measure temperature.

🎯 Exam Tip: Remember the standard units of measurement for common physical properties, such as Celsius for temperature.

Question 10. Nowadays, ................ thermometers are frequently used.
Answer: digital
In simple words: Digital thermometers are now commonly used for their ease of reading and accuracy.

🎯 Exam Tip: Be aware of modern applications and advancements in common measuring tools.

Question 11. Solids have a shape of its ............... .
Answer: own
In simple words: Solids possess their own distinct and unchanging shape.

🎯 Exam Tip: A key characteristic of solids is their definite shape; liquids and gases do not have their "own" shape.

Question 12. Solids have a ............... volume.
Answer: definite
In simple words: Solids maintain a fixed and specific volume.

🎯 Exam Tip: Understand that solids have both a definite shape and a definite volume, unlike liquids (definite volume, indefinite shape) and gases (indefinite shape, indefinite volume).

Question 13. Liquids take the shape of the ........... .
Answer: container
In simple words: Liquids conform to the shape of whatever container they are in.

🎯 Exam Tip: This highlights a fundamental property of liquids: their indefinite shape.

Question 14. Liquids have a ............... volume.
Answer: specific
In simple words: Liquids occupy a fixed, specific amount of space, known as their volume.

🎯 Exam Tip: While liquids don't have a fixed shape, they do have a definite or specific volume.

Question 15. Air occupies all the available ............... .
Answer: space
In simple words: Air, being a gas, will expand to fill every bit of the space it is given.

🎯 Exam Tip: Gases are characterized by occupying the entire volume of their container due to their indefinite shape and volume.

Question 16. Evaporation occurs from the ............... of the water.
Answer: surface
In simple words: Evaporation primarily happens from the top layer, or surface, of water.

🎯 Exam Tip: Remember that evaporation is a surface phenomenon, distinguishing it from boiling which occurs throughout the liquid.

Question 17. At sea-level, pure water boils at ............... .
Answer: 100°C
In simple words: Pure water changes to steam at a temperature of 100 degrees Celsius when at sea-level.

🎯 Exam Tip: Know the standard boiling point of water at atmospheric pressure (sea-level) as 100°C.

Question 18. Condensation of steam takes place at ............... .
Answer: 100°C
In simple words: Steam turns back into liquid water at 100 degrees Celsius, which is its condensation point.

🎯 Exam Tip: The condensation point of a substance is numerically equal to its boiling point.

Question 19. The temperature of a substance can fall below ............... .
Answer: 0°C
In simple words: A substance's temperature can drop to levels colder than zero degrees Celsius.

🎯 Exam Tip: Recognize that temperatures can go below freezing point, often requiring specific cooling mechanisms.

Question 20. Ice melts at ............... .
Answer: 0°C
In simple words: Ice changes into liquid water at a temperature of zero degrees Celsius.

🎯 Exam Tip: Know the standard melting point of ice (which is the freezing point of water) as 0°C.

Question 21. Each substance has a specific boiling point which is also its ............... point.
Answer: condensation
In simple words: Every substance has a unique boiling point, which is also the exact temperature at which it condenses back into a liquid.

🎯 Exam Tip: It's important to know that for a pure substance, the boiling point is identical to its condensation point.

Question 22. Each substance has a specific melting point which is the same as its ............... point.
Answer: freezing
In simple words: For any given substance, its melting point (where it turns liquid from solid) is the same temperature as its freezing point (where it turns solid from liquid).

🎯 Exam Tip: Remember that the melting point and freezing point of a pure substance are the same temperature.

Question 23. Candles are made by melting ............... wax.
Answer: paraffin
In simple words: Candles are produced by melting and shaping paraffin wax.

🎯 Exam Tip: Identify paraffin wax as the primary material for manufacturing candles.

Question 24. Solid carbon-dioxide is ............... .
Answer: dry ice
In simple words: Solid carbon-dioxide is commonly known as dry ice.

🎯 Exam Tip: Know the common name for solid carbon dioxide and its property of sublimation.

Question 25. Liquid ............... is used in animal husbandry.
Answer: nitrogen
In simple words: Liquid nitrogen is utilized in animal husbandry, typically for preserving biological samples.

🎯 Exam Tip: Recognize the specific application of liquid nitrogen in fields like animal husbandry due to its extremely low temperature.

Question 26. Sand is melted to make ............... .
Answer: glass
In simple words: When sand is heated to a very high temperature and melted, it can be transformed into glass.

🎯 Exam Tip: Understand that sand (silica) is the primary raw material for making glass through a melting process.

Question 27. Iron is melted to make ............... .
Answer: tools
In simple words: Iron is melted and shaped to create various tools due to its strength and durability.

🎯 Exam Tip: Connect the melting and shaping of iron directly to the production of useful tools, leveraging its robust properties.

Question 28. Substances can be identified by studying their ............... .
Answer: properties
In simple words: We can tell one substance from another by examining its unique characteristics or properties.

🎯 Exam Tip: Identifying substances relies on observing and understanding their distinct physical and chemical properties.

Question 29. Substances that break into small particles are said to be ............... .
Answer: brittle
In simple words: Materials that easily shatter or break into smaller pieces are described as brittle.

🎯 Exam Tip: Brittleness is a key material property describing a substance's tendency to fracture under stress rather than deform.

Question 30. The ............... of any liquid is determined by how easily it flows.
Answer: fluidity
In simple words: A liquid's fluidity refers to how readily it flows.

🎯 Exam Tip: Fluidity is a direct measure of a liquid's ability to flow, with lower viscosity liquids having higher fluidity.

Question 31. Between substances of the same volume, the ones with greater density are ............... than those of lesser density.
Answer: heavier
In simple words: For the same amount of space, substances with higher density will weigh more than those with lower density.

🎯 Exam Tip: Understand that density relates mass to volume, so a denser object with the same volume will be heavier.

Question 32. The property of a substance of getting ............... is called its solubility.
Answer: dissolved
In simple words: Solubility is the ability of a substance to mix completely and form a solution with a liquid.

🎯 Exam Tip: Define solubility as the capacity of a solute to dissolve in a solvent to form a homogeneous solution.

Question 37. Every metal has a ............... colour by which it can be identified.
Answer: specific
In simple words: Each metal has a distinct color that helps us recognize it.

🎯 Exam Tip: Recognizing specific properties like color for metals is crucial for identification and material science applications.

Question 38. Metals produce ............... sound.
Answer: ringing
In simple words: Metals make a ringing sound when struck, a property known as sonority.

🎯 Exam Tip: Sonority is a key characteristic of metals, often used in making bells and musical instruments.

Question 39. Metals form a ....... group of substances.
Answer: separate
In simple words: Metals belong to their own distinct category of elements with unique shared characteristics.

🎯 Exam Tip: Understanding that metals are a distinct group helps in classifying elements based on their properties.

Question 40. Heat is the cause of the change of the state of ............... .
Answer: substances
In simple words: Adding or removing heat is what causes substances to change between solid, liquid, and gas states.

🎯 Exam Tip: Heat energy plays a fundamental role in the phase transitions of all matter, a core concept in physical science.

Match The Columns:

Question 1. Match the columns:

Column 'A'	Column 'B'
1. Boiling water	a. > 35° C
2. Body temperature	b. 0° C
3. Freezing water	c. < 5° C
4. Air (summer afternoon)	d. < 15° C
5. Inside a fridge	e. < -18° C
6. Air (winter night)	f. 100° C
7. Inside the freezer	g. 37°C

Answer:

Column 'A'	Column 'B'
1. Boiling water	f. 100° C
2. Body temperature	g. 37°C
3. Freezing water	b. 0° C
4. Air (summer afternoon)	a. > 35° C
5. Inside a fridge	c. < 5° C
6. Air (winter night)	d. < 15° C
7. Inside the freezer	e. < -18° C

In simple words: This exercise matches common phenomena or locations with their typical temperature ranges in Celsius, helping to understand temperature scales in everyday contexts.

🎯 Exam Tip: Accurately associating physical states and environments with their characteristic temperatures is essential for practical application of thermal concepts.

Answer In One Sentence:

Question 1. What is change of state of substances?
Answer: When a substance changes from one state to another, the process is called change of state of the substance.
In simple words: A change of state occurs when a substance transforms from a solid to a liquid, a liquid to a gas, or vice versa.

🎯 Exam Tip: Understanding the basic definition of change of state is foundational for studying physical properties of matter.

Question 2. When does state of substance change?
Answer: State of substance changes when it is heated or cooled.
In simple words: Substances change their state when they either gain heat (are heated) or lose heat (are cooled).

🎯 Exam Tip: Remember that energy input (heating) or removal (cooling) is the driving force behind all phase changes.

Question 3. In which state do substances exist in our surroundings?
Answer: The substances exist in solid, liquid and gaseous form in our surroundings.
In simple words: In our environment, substances can be found in three main forms: solid, liquid, or gas.

🎯 Exam Tip: Most matter around us exists in one of these three common physical states.

Question 4. What happens when a substance gains heat?
Answer: When a substance gains heat, it changes its state i.e. from solid to liquid and liquid to gas.
In simple words: Gaining heat causes a substance to melt from solid to liquid, or vaporize from liquid to gas.

🎯 Exam Tip: Heat absorption leads to increased kinetic energy of particles, facilitating phase transitions to higher energy states.

Question 5. What happens when a substance loses heat?
Answer: When a substance loses heat, it changes its state from gaseous to liquid and liquid to solid state.
In simple words: When a substance loses heat, it condenses from gas to liquid, or freezes from liquid to solid.

🎯 Exam Tip: Heat release causes a decrease in kinetic energy, resulting in phase transitions to lower energy states.

Question 6. How do we tell how hot or cold a substance is?
Answer: The temperature on the thermometer will tell us how hot or cold a substance is.
In simple words: We use a thermometer to measure and determine the exact hotness or coldness, also known as the temperature, of a substance.

🎯 Exam Tip: A thermometer provides an objective and quantitative measure of temperature, unlike subjective human perception.

Question 7. What is the unit of measuring temperature.
Answer: Degrees Celsius (°C) is the unit of measuring temperature.
In simple words: Temperature is typically measured using the unit of Degrees Celsius, represented as °C.

🎯 Exam Tip: Celsius is the most common unit for temperature measurement in scientific contexts and most countries.

Question 8. What is the boiling point of water?
Answer: The boiling point of water is 100° C.
In simple words: Water boils and turns into steam at a temperature of 100 degrees Celsius at standard atmospheric pressure.

🎯 Exam Tip: Knowing the boiling point of water is a fundamental reference point in understanding phase changes and temperature scales.

Question 9. What is condensation?
Answer: When vapour cools, it is converted into liquid again. This process is condensation.
In simple words: Condensation is when a gas or vapor cools down and changes back into a liquid state.

🎯 Exam Tip: Condensation is the reverse process of vaporization and involves the release of heat energy.

Question 10. At what temperature condensation of steam takes place?
Answer: Condensation of steam takes place at 100° С.
In simple words: Steam begins to condense and turn back into liquid water at 100 degrees Celsius, the same temperature as its boiling point.

🎯 Exam Tip: The condensation point of a substance is numerically equal to its boiling point under the same pressure conditions.

Question 11. What is the freezing point of water?
Answer: 0° C is the freezing point of water.
In simple words: Water freezes and turns into ice at a temperature of 0 degrees Celsius.

🎯 Exam Tip: The freezing point of water is another crucial reference point for temperature and phase changes.

Question 12. What is the temperature of air in the freezer of a refrigerator?
Answer: -18° C is the temperature of air in the freezer of a refrigerator.
In simple words: The air inside a typical freezer is maintained at a very low temperature, usually around -18 degrees Celsius, to keep food frozen.

🎯 Exam Tip: Freezers operate at temperatures significantly below freezing point to ensure proper preservation of food items.

Question 13. At what temperature ice melts?
Answer: Ice melts at 0° C.
In simple words: Ice changes from a solid state back into liquid water at 0 degrees Celsius.

🎯 Exam Tip: The melting point of a substance is numerically equal to its freezing point.

Question 14. How are candles made?
Answer: Candles are made by melting paraffin wax.
In simple words: Candles are formed by heating paraffin wax until it becomes liquid, then molding it around a wick as it cools and solidifies.

🎯 Exam Tip: This process demonstrates how a change of state (melting and solidification) is utilized in manufacturing everyday items.

Question 15. What is the use of solid carbon-dioxide?
Answer: Solid carbon-dioxide (dry ice) is used to make ice cream and to keep it frozen.
In simple words: Solid carbon dioxide, also known as dry ice, is primarily used to keep things very cold and frozen, especially ice cream, because it sublimes without leaving liquid residue.

🎯 Exam Tip: Dry ice is valued for its extremely low temperature and the property of sublimation, making it an excellent refrigerant.

Question 16. What is the use of liquid nitrogen?
Answer: Liquid nitrogen is used in animal husbandry.
In simple words: Liquid nitrogen, due to its extremely low temperature, is used in animal husbandry for preserving genetic material like semen and embryos.

🎯 Exam Tip: Cryopreservation using liquid nitrogen is a vital technique in various fields, including biology and medicine, due to its very low temperature.

Question 17. What is sublimation?
Answer: The change of a solid substance directly into gas or vapour without changing into a liquid is called sublimation.
In simple words: Sublimation is the direct transformation of a solid into a gas, bypassing the liquid phase entirely.

🎯 Exam Tip: Recognize common examples like dry ice and camphor to illustrate sublimation, a unique phase transition.

Question 18. Define brittleness / What is brittleness?
Answer: Some substances break into small pieces or particles. Such substances are said to be brittle. This property of substances is called brittleness.
In simple words: Brittleness is the property of a material that causes it to break easily into small pieces when a force is applied, rather than bending or deforming.

🎯 Exam Tip: Materials like glass and chalk are classic examples of brittle substances, important for material selection in engineering.

Question 19. Define hardness / What is hardness?
Answer: The hardness of a substance is determined by how much resistance it offers to the substances being pushed through it.
In simple words: Hardness is a material's ability to resist indentation, scratching, or abrasion when another object tries to penetrate or mark its surface.

🎯 Exam Tip: Hardness is a critical property for tools and protective surfaces, measured by various scales like Mohs or Vickers.

Question 20. Define elasticity / What is elasticity?
Answer: Some substances change their shape when a force is applied on them but return to their original shape and size when the force is removed. This property is called elasticity.
In simple words: Elasticity is the ability of a material to deform under stress and then return to its original shape once the stress is removed.

🎯 Exam Tip: Rubber bands and springs are common examples that clearly demonstrate the property of elasticity.

Question 21. Define fluidity / What is fluidity?
Answer: Liquids flow downward on a sloping surface. This property is called fluidity.
In simple words: Fluidity is the characteristic of a substance, typically a liquid or gas, to flow easily and take the shape of its container.

🎯 Exam Tip: Fluidity is inversely related to viscosity; the more fluid a substance, the less viscous it is.

Question 22. How is fluidity of any liquid determined?
Answer: Fluidity of any liquid is determined by how easily it flows.
In simple words: The fluidity of a liquid is assessed by observing how readily and quickly it pours or moves.

🎯 Exam Tip: Liquids with lower viscosity, like water, demonstrate higher fluidity compared to highly viscous liquids, like honey.

Question 23. Define density / What is density?
Answer: The mass of different substances having the same volume can be different. This difference is because of the difference in their densities. Between substances of the same volume, the ones with greater density are heavier than those of lesser density.
In simple words: Density is a measure of how much mass is contained in a given volume of a substance, indicating how "packed" its matter is.

🎯 Exam Tip: Density is calculated as mass divided by volume (\( \rho = m/V \)) and helps explain why some objects float while others sink.

Question 24. Define solubility / What is solubility?
Answer: The property of a substance of getting dissolved is called its solubility.
In simple words: Solubility is the ability of a substance (solute) to dissolve into another substance (solvent) to form a uniform mixture called a solution.

🎯 Exam Tip: Temperature often affects solubility; for most solids, solubility increases with temperature, while for gases, it decreases.

Question 25. Define transparency / What is transparency?
Answer: When we can look through a substance and see things on the other side, then that substance is said to be transparent. This property of the substances is called transparency.
In simple words: Transparency is the property of a material that allows light to pass through it, enabling objects on the other side to be clearly seen.

🎯 Exam Tip: Transparent materials like glass are crucial for applications requiring clear vision, such as windows and lenses.

Question 26. List some transparent substances.
Answer: Glass, air, clean water and some types of plastic are transparent substances.
In simple words: Common transparent substances include glass, the air we breathe, pure water, and certain kinds of plastic.

🎯 Exam Tip: Identifying transparent substances helps in understanding light interaction with different materials.

Question 27. What are metals?
Answer: Metals are substances like copper, gold, iron, aluminium. They are found in the form of minerals deep inside the earth. Minerals from the earth's crust are processed to obtain metals.
In simple words: Metals are a class of elements, like iron or gold, typically found as minerals in the Earth, which are then processed to extract the pure metal.

🎯 Exam Tip: Metals are distinguished by properties like luster, conductivity, malleability, and ductility, making them valuable for various uses.

Question 28. Define malleability. / What is malleability?
Answer: Metals can be converted into sheets by hammering. This property of metals is called malleability.
In simple words: Malleability is the property of a material, especially metals, to be hammered or pressed into thin sheets without breaking.

🎯 Exam Tip: Gold is an excellent example of a highly malleable metal, allowing it to be shaped into intricate designs and foils.

Question 29. Define ductility. / What is ductility?
Answer: Metals can be stretched and drawn into thin wires. This property of metals is called ductility
In simple words: Ductility is the ability of a material, particularly metals, to be stretched into thin wires without losing toughness or breaking.

🎯 Exam Tip: Copper's high ductility makes it ideal for electrical wiring, showcasing the practical importance of this property.

Question 30. Name some ductile metals.
Answer: Metals like silver, gold, platinum can be drawn into fine wires.
In simple words: Silver, gold, and platinum are examples of metals that are highly ductile, meaning they can be easily stretched into thin wires.

🎯 Exam Tip: Remember these examples to illustrate the concept of ductility and its application in industries like jewelry and electronics.

Question 31. Define electrical conductivity. / What is electrical conduction?
Answer: Electricity flows through metals. All metals are conductors of electricity to a greater or lesser extent.
In simple words: Electrical conductivity is the ability of a material to allow electric current to pass through it, with metals being good conductors.

🎯 Exam Tip: High electrical conductivity makes metals essential for electrical circuits and power transmission.

Question 32. Define thermal conductivity. / What is thermal conductivity?
Answer: Metals allow heat to flow through them. This property is called thermal conductivity
In simple words: Thermal conductivity is the measure of a material's ability to transfer heat energy through it.

🎯 Exam Tip: Materials with high thermal conductivity are used in heat sinks and cooking utensils, while insulators have low thermal conductivity.

Question 33. What is lustre?
Answer: The typical shine or characteristic colour by which metal can be identified is called lustre.
In simple words: Lustre refers to the characteristic shiny appearance or unique color that metals possess, making them easily identifiable.

🎯 Exam Tip: Metallic luster is a distinguishing physical property of metals, often described as shiny or reflective.

Question 34. What is sonority of metals? / Define sonority.
Answer: Metals produce a ringing sound. This property is called the sonority of metals.
In simple words: Sonority is the property of metals to produce a clear, ringing sound when struck, often associated with bells.

🎯 Exam Tip: Sonority is a key reason why metals are used in musical instruments and bells.

Give Scientific Reasons For Following:

Question 1. Metals are used to make musical instruments.
Answer: Metals possess the property of being sonorous, i.e. produce a ringing sound. Hence, they are used to make musical instruments.
In simple words: Metals are chosen for musical instruments because their sonorous property allows them to produce clear, ringing sounds when vibrated.

🎯 Exam Tip: Link the property of sonority directly to the function of musical instruments to explain the "why."

Question 2. Ornaments are made up of metals.
Answer: Metals have the property of being malleable, ductile, lustrous. Hence, ornaments are made up of metals.
In simple words: Metals like gold and silver are used for ornaments because they can be easily shaped (malleable), drawn into wires (ductile), and have an attractive shine (lustrous).

🎯 Exam Tip: Highlight the combined properties (malleability, ductility, luster) that make metals ideal for jewelry and decorative items.

Question 3. Why should we not put our hand or finger in the water to judge the hotness of water?
Answer: We should never put our hand or finger in the water to judge how hot it is because that is not an accurate measure. Besides if the substance is very hot, we could get scalded.
In simple words: Using hands to check water temperature is unreliable and dangerous, as it can lead to burns if the water is too hot, and doesn't give an accurate reading.

🎯 Exam Tip: Always prioritize safety and use appropriate measuring tools (like a thermometer) for accurate scientific observations.

Can You Tell?

Question 1. Why are electric boards fitted on the wall made of plastic or wood?
Answer: Plastic or wood are bad conductors of heat and electricity. Electric boards are made up of plastic or wood. So that while touching we will not get electric shock.
In simple words: Electric boards are made from plastic or wood because these materials are poor conductors of electricity, preventing electric shocks when touched.

🎯 Exam Tip: Emphasize the insulating property of plastic and wood as the primary reason for their use in electrical safety components.

Question 2. The handle of cooker is made of plastic. Why?
Answer: Cooker is made of metal. When food is cooked in it, it gets heated and the whole of its body becomes hot due to thermal conductivity. Hence with the plastic handle we can easily lift the hot cooker as plastic is a bad conductor of heat.
In simple words: A cooker's handle is made of plastic because plastic is a poor conductor of heat, preventing the handle from getting hot and allowing you to safely lift the cooker even when its metal body is hot.

🎯 Exam Tip: This illustrates the practical application of thermal insulation in everyday items to ensure safety and convenience.

Question 3. Use your brain power! On opening a box of camphor, its smell spreads all around. Why does this happen?
Answer:1. Camphor is a sublimate substance. 2. When a box of camphor is opened it changes its state from solid to gas or vapour state. 3. This change takes due to the process of sublimation where camphor absorbs heat from surrounding to change from solid to gaseous state. 4. Camphor particles in gaseous state start spreading all around. 5. Hence on opening a box of camphor its smell spreads all around.
In simple words: Camphor's smell spreads because it undergoes sublimation, turning directly from a solid into a gas at room temperature. The gas particles then diffuse rapidly throughout the air, carrying the scent everywhere.

🎯 Exam Tip: This question highlights sublimation and diffusion, two important concepts related to the behavior of particles in different states of matter.

Question 4. Identify the objects shown in fig. 5.14. From which substances are they made? What are these substances called as a group?
Answer: In fig 5.14, the metallic bars are shown, these bars are made up of shiny solid. These substances are called metals.
In simple words: The image displays metallic bars made from shiny, solid materials, which are collectively identified as metals.

🎯 Exam Tip: Be able to identify common materials and classify them into broad categories like metals based on their observable properties.

Question 5. Name the solid, liquid and gaseous states of water.
Answer:
• Solid- Ice
• Liquid - water
• Gas – water vapour.
In simple words: The three states of water are ice (solid), water (liquid), and water vapor (gas).

🎯 Exam Tip: These three common states of water serve as primary examples for understanding solid, liquid, and gaseous phases of matter.

Question 6. Read this list of substances: spirit, camphor, petrol, ghee, coconut oil, naphthalene balls, ammonium chloride (navsagar).
(a) Which one freezes in winter?
Answer: Coconut oil, ghee.
In simple words: Coconut oil and ghee solidify in cold winter temperatures because their freezing points are relatively high compared to typical winter ambient temperatures.

🎯 Exam Tip: This question tests knowledge of freezing points and how substances react to common temperature changes.

Question 6. (b) Which liquids have you seen change into a vapour?
Answer: Spirit, petrol.
In simple words: Spirit and petrol readily convert into vapor at room temperature due to their volatile nature, meaning they evaporate easily.

🎯 Exam Tip: Volatile liquids have low boiling points and high vapor pressures, making them evaporate quickly.

Question 6. (c) Which solid directly changes into gaseous state?
Answer: Camphor, naphthalene balls, ammonium chloride.
In simple words: Camphor, naphthalene balls, and ammonium chloride are solids that directly turn into a gas without becoming a liquid first, a process called sublimation.

🎯 Exam Tip: These are classic examples of substances that exhibit sublimation, important to remember for understanding phase changes.

Question 7. The chart given below shows the boiling point and freezing point of some substances. State whether these substances are solid, liquid or gaseous at room temperature.

Substance	Freezing Point	Boiling Point
Candle	60 °C	350 °C
Plastic	> 250 °C	954 °C
Iron	1535 °C	2862 °C

Answer: Candle, plastic and iron are in solid state at room temperature.
In simple words: At typical room temperature (around 20-25°C), candle wax, plastic, and iron are all in their solid state because room temperature falls below their respective freezing points.

🎯 Exam Tip: To determine a substance's state at room temperature, compare room temperature to its freezing and boiling points; if it's below freezing, it's solid; if between, it's liquid; if above boiling, it's gas.

Distinguish Between Solids, Liquids And Gases:

Question. Distinguish between solids, liquids and gases.
Answer:

Solids	Liquid	Gases
e.g.: A piece of iron	e.g.: Water, spirit, oil	e.g.: Air
Has a shape of its own, Retains shape, no matter how it is kept.	Does not have a shape of its own. Takes the shape of the container.	Does not have a shape of its own. Occupies all the available space.
Has a definite volume. Solids like sugar, sand when poured on a flat surface, form a heap.	It has a specific volume. Occupies definite portion of a container. Spreads on a flat surface on pouring. Flows downwards along a slope. Takes the shape of the surface.	Does not have a definite volume. On changing the pressure on a gas in a closed container, its volume also changes.

In simple words: Solids have fixed shape and volume; liquids have fixed volume but take the container's shape; gases have neither fixed shape nor volume, expanding to fill any container.

🎯 Exam Tip: Understanding the differences in shape, volume, and particle arrangement is fundamental to distinguishing between the three primary states of matter.

Distinguish Between Boiling And Melting:

Question. Distinguish between Boiling and Melting.
Answer:

Boiling	Melting
1. When heat is supplied to liquids, they boil.	1. When heat is supplied to solids, they melt.
2. Boiling leads liquids to vapour/gaseous state.	2. Melting leads solids to liquid state.
3. The temparature at which liquid starts boiling continuously is called boiling point.	3. The temperature at which solid turns to liquid completely is called melting point.

In simple words: Boiling is when a liquid rapidly turns into a gas, while melting is when a solid turns into a liquid, both occurring at specific temperatures when heat is added.

🎯 Exam Tip: Clearly differentiate between boiling (liquid to gas throughout) and melting (solid to liquid) as distinct phase change processes, each with its own characteristic temperature.

Answer The Following Briefly:

Question 1. List properties of solids
Answer:1. Solids have its own shape i.e. Retains shape, no matter how it is kept. 2. Solids have definite volume. 3. e.g. Sand when poured on a flat surface form a heap.
In simple words: Solids maintain their own fixed shape and definite volume, and unlike liquids, they form a heap when poured, rather than spreading out.

🎯 Exam Tip: Focus on the fixed shape and volume as the defining characteristics of solids, which distinguishes them from liquids and gases.

Question 2. List properties of liquids.
Answer:1. Liquid does not have a shape of its own. Takes the shape of the container. 2. A liquid has a specific volume i.e. occupies definite portion of a container. 3. Liquids: e.g. water, milk, kerosene.
In simple words: Liquids have a definite volume but no fixed shape, always taking on the shape of their container.

🎯 Exam Tip: Remember that liquids flow, have a constant volume, and their shape is determined by the vessel they are in.

Question 3. List properties of gases.
Answer:1. Gases does not have a shape of its own. 2. Occupies all the available space. 3. Does not have a definite volume. 4. e.g. Air.
In simple words: Gases have no definite shape or volume, expanding to fill any container they occupy, and their particles are far apart.

🎯 Exam Tip: The lack of fixed shape and volume, along with particles that fill all available space, are the key identifying features of gases.

Question 4. Explain with example how liquids take the shape of the surface.
Answer: Liquids have a specific volume. They occupy definite portion of a container. Liquids spreads on a flat surface on pouring. Liquids flow downwards along a slope.
In simple words: Liquids conform to the shape of their container or surface because their particles can move freely past each other, allowing them to flow and spread out.

🎯 Exam Tip: Use examples like water poured into a glass or spilled on a table to vividly illustrate how liquids adapt to their surroundings.

Question 5. Explain Ebullition.
Answer:1. As the water gets heated, its temperature increases and it evaporates at a faster and faster rate. 2. When water kept on a stove attains a particular temperature or level of heat, then evaporation takes place in all parts of the body of water. 3. Then we see water bubbles rising at a faster and faster rate to the surface and steam mixing in the air. 4. This is called boiling of water or Ebullition.
In simple words: Ebullition, or boiling, is the rapid vaporization of a liquid that occurs throughout the liquid when it reaches its boiling point, characterized by bubbles of vapor forming and rising to the surface.

🎯 Exam Tip: Ebullition is distinct from evaporation, as it occurs throughout the bulk of the liquid at a specific temperature, unlike surface evaporation at any temperature.

Question 6. Explain: Boiling point and condensation point of water are one and the same.
Answer: Water boils at 100°C. i.e. boiling point of water is 100°C. Condensation of steam also takes place at 100° C. Thus boiling point and condensation point of water are one and the same.
In simple words: The boiling point and condensation point of water are both 100°C because boiling is the process of a liquid turning into a gas, and condensation is the reverse process of that same gas turning back into a liquid, both occurring at the same critical temperature.

🎯 Exam Tip: Emphasize that these two phase transitions are reversible and occur at the same temperature under given pressure conditions, representing an equilibrium state.

Question 7. Explain freezing point of water.
Answer:1. Water kept in a fridge or on ice becomes cooler and cooler i.e. its temperature falls. 2. At a certain temperature water does not cool further but starts freezing and forms ice. 3. The temperature at which this happens is called the freezing point of water. (0° C)
In simple words: The freezing point of water is 0°C, the temperature at which liquid water turns into solid ice as it loses heat, and its temperature stops dropping until all water is frozen.

🎯 Exam Tip: The freezing point is a constant temperature during the phase change from liquid to solid, where both phases can coexist.

Question 8. Explain: Freezing point and melting point of water are same.
Answer:1. The temperature at which water does not get any cooler but starts freezing and forming ice is 0° C. 2. When ice gets heat, it starts melting or changes into liquid state at 0° C. 3. Thus, freezing point and melting point of water are one and the same.
In simple words: The freezing point (liquid to solid) and melting point (solid to liquid) of water are identical at 0°C because these are reverse processes occurring at the same temperature under equilibrium conditions.

🎯 Exam Tip: Highlight that for any pure substance, the melting point and freezing point are the same, representing the temperature at which solid and liquid phases are in equilibrium.

Question 9. List various uses of changes in physical state.
Answer:
1. Candles are made by melting paraffin wax.
2. Solid carbon-dioxide (dry ice) is used to make ice-cream and to keep it frozen.
3. Liquid nitrogen is used in animal husbandry.
4. Sand (silica) is melted to make glass.
5. Metals like gold and silver are melted to make ornaments.
6. Iron is melted to make tools.
In simple words: Physical state changes are utilized to create various products like candles from wax, preserve items with dry ice or liquid nitrogen, and form glass, ornaments, and tools from melted sand and metals.

🎯 Exam Tip: Listing specific examples for each use of physical state change is crucial for full marks.

Question 10. List the properties of substances:
Answer: The properties of substances are
1. Brittleness
2. Hardness
3. Elasticity
4. Fluidity
5. Density
6. Solubility
7. Transparency
In simple words: Substances have properties like brittleness (how easily they break), hardness (resistance to deformation), elasticity (ability to regain shape), fluidity (ability to flow), density (mass per volume), solubility (ability to dissolve), and transparency (ability to let light pass through).

🎯 Exam Tip: Clearly define and list the key physical properties of substances for a comprehensive answer.

Question 11. List properties of metals:
Answer: The properties of metals are
1. Malleability
2. Ductility
3. Electrical conductivity
4. Thermal conductivity
5. Lustre
6. Sonority
In simple words: Metals exhibit malleability (can be hammered into sheets), ductility (can be drawn into wires), electrical and thermal conductivity (conduct electricity and heat), lustre (shininess), and sonority (produce ringing sound).

🎯 Exam Tip: Remember to list both the physical and chemical properties of metals, focusing on their practical applications.

Question 12. How can we change the volume of a gas?
Answer: On changing the pressure on a gas in a closed container we can change its volume.
In simple words: The volume of a gas in a sealed container can be altered by increasing or decreasing the pressure applied to it.

🎯 Exam Tip: Understanding the inverse relationship between pressure and volume for gases is fundamental for this concept.

Can You Tell?

Question 1. Does water change into vapour the moment we place the vessel on a stove? Does water kept in fridge change at once into ice?
Answer: No, it doesn't. Water slowly changes from one state to another.
In simple words: State changes for water, like evaporation or freezing, do not happen instantly; they occur gradually over time as heat is gained or lost.

🎯 Exam Tip: Focus on explaining the gradual nature of phase transitions and the energy required for these changes.

Question 2. How do we tell how hot or cold a substance is?
Answer: A thermometer is used to measure the temperature of the subatance which tell us hot or cold it is.
In simple words: We determine the hotness or coldness of a substance by measuring its temperature using a thermometer.

🎯 Exam Tip: Emphasize the importance of using accurate measuring instruments like a thermometer for objective assessment of temperature.

Question 3. How will you identify the following
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र तीन अलग-अलग वस्तुओं को दर्शाता है: पहला, ढेर सारी लोहे की छड़ें; दूसरा, एक ढेर में रखा हुआ सफेद पाउडर; और तीसरा, एक लकड़ी का दरवाजा। ये चित्र विभिन्न पदार्थों और वस्तुओं की पहचान करने के संदर्भ में दिए गए हैं।

Question i. A glass: Is it made of plastic, steel or glass?
Answer: Glass is made of glass as it is transparent.
In simple words: A glass is made of glass because of its characteristic transparency, which allows light to pass through.

🎯 Exam Tip: When identifying materials, consider their defining properties such as transparency, opacity, or density.

Question ii. A rod: Iron or aluminium.
Answer: A rod is made of iron as it is heavy.
In simple words: Given a choice between iron and aluminum, a heavy rod is likely made of iron due to its higher density compared to aluminum.

🎯 Exam Tip: Density is a key property used to distinguish between different metals or substances of the same volume.

Question iii. A door: Wooden or glass?
Answer: A door is wooden as it is opaque.
In simple words: A door is typically made of wood because wood is opaque, providing privacy and blocking light, unlike transparent glass.

🎯 Exam Tip: The function and required properties (like opacity for privacy) often determine the material used for an object.

Question iv. A white powder: Salt or chalk powder?
Answer: If powder dissloves in water it is salt and if it does not dissolves in water it is chalk.
In simple words: To distinguish between salt and chalk powder, test their solubility in water; salt will dissolve, while chalk powder will not.

🎯 Exam Tip: Solubility is a crucial physical property that helps differentiate between various white powders.