Maharashtra Board Class 7 Science Chapter 3 Properties of Natural Resources Solutions

Fill In The Blanks With The Appropriate Term.

Question 1. The capacity of air to hold moisture depends upon the ............... of the air.
Answer: temperature
In simple words: The amount of moisture air can hold is affected by its temperature. Warmer air generally holds more moisture than colder air.

🎯 Exam Tip: Understanding the relationship between temperature and air's moisture capacity is crucial for explaining humidity and weather phenomena.

Question 2. Water does not have a ............... but has definite ............ and ............ .
Answer: shape, volume, mass
In simple words: Water takes the shape of its container but always has a specific amount of space it occupies and a consistent quantity of matter.

🎯 Exam Tip: This question tests fundamental properties of liquids, distinguishing them from solids and gases in terms of shape, volume, and mass.

Question 3. While freezing, the ............... of water is lowered.
Answer: density
In simple words: When water freezes, its density decreases because it expands and takes up more space as ice.

🎯 Exam Tip: The anomalous expansion of water upon freezing is a key concept; remember that ice is less dense than liquid water, which explains why it floats.

Question 4. ............... soil has pH 7.
Answer: neutral
In simple words: Soil with a pH of 7 is considered neutral, meaning it is neither acidic nor alkaline.

🎯 Exam Tip: Knowing the pH scale for soil (7 is neutral, below 7 is acidic, above 7 is alkaline) is important for understanding soil fertility and plant growth requirements.

2. Why Is The Said That -

Question. a. Air is a homogeneous mixture of various gases.
Answer: 1. Air is made of oxygen, nitrogen, carbondioxide, water vapour and dust particles. 2. All these are in different proportions. Therefore air is a mixture.
In simple words: Air contains different gases like oxygen and nitrogen, which are evenly mixed throughout, making it a homogeneous mixture. Even though proportions can vary slightly, it generally appears uniform.

🎯 Exam Tip: Focus on the definition of a homogeneous mixture (uniform composition) and list the primary components of air to score well.

Question. b. Water is a universal solvent.
Answer: 1. Water dissolves more substances than any other liquid. It dissolves solids, other liquids and even gases in it. Therefore, it is called as Universal solvent. 2. Water is used as a solvent in factories, laboratories, foodstuffs and in various types of biological processes occurring in the body such as digestion, excretion, etc.
In simple words: Water is called a universal solvent because its unique molecular structure allows it to dissolve a wide variety of substances, essential for many natural and biological processes.

🎯 Exam Tip: Highlight water's ability to dissolve solids, liquids, and gases, and provide examples of its use in both industrial and biological contexts.

Question. c. There is no alternative to water for cleaning purposes.
Answer: Water is a universal solvent. It dissolves more substances than any other liquid so there is no alternative to water for cleaning purposes.
In simple words: Due to its exceptional ability to dissolve a vast range of substances, water remains irreplaceable for most cleaning applications.

🎯 Exam Tip: Link water's universal solvent property directly to its effectiveness and indispensability for cleaning, making it hard to replace.

3. What Will Happen If-

Question. a. The amount of water vapour in the air increases.
Answer: We feel the dampness or the humidity.
In simple words: An increase in water vapor in the air leads to higher humidity, making us feel damp and sticky.

🎯 Exam Tip: This question assesses understanding of humidity; remember that more water vapor equals higher humidity and a feeling of dampness.

Question. b. Only one crop is grown repeatedly in the soil.
Answer: The fertility of the soil decreases.
In simple words: Continuously growing the same crop depletes specific nutrients from the soil, leading to a significant reduction in its overall fertility over time.

🎯 Exam Tip: Emphasize nutrient depletion as the main reason for decreased soil fertility when practicing monocropping; crop rotation is a common solution.

4. With Whom Should I Pair Up?

Question. a.

Answer:

In simple words: Air scatters light, water is essential for excretion, and soil has the property of plasticity.

🎯 Exam Tip: For matching questions, understand the unique properties or primary uses associated with each item in Column 'A' to correctly pair it with Column 'B'.

5. State Whether The Following Statements Are True Or False.

Question. a. Sandy soil has low capacity for holding water.
Answer: True
In simple words: Sandy soil has large particles and large spaces between them, allowing water to drain quickly, resulting in low water retention.

🎯 Exam Tip: Remember that sandy soil's coarse texture leads to poor water retention, which is a key characteristic to describe its suitability for different plants.

Question. b. Sea water is a bad conductor of electricity.
Answer: False. Sea water is a good conductor of electricity
In simple words: Sea water contains dissolved salts, which break into ions and allow it to conduct electricity effectively, making it a good conductor.

🎯 Exam Tip: The presence of dissolved salts (electrolytes) in seawater makes it a good conductor; pure water, in contrast, is a poor conductor.

Question. c. The substance in which a solute dissolves is called a solvent.
Answer: True
In simple words: A solvent is the substance that dissolves another substance, called the solute, to form a solution.

🎯 Exam Tip: Clearly define solvent and solute, noting that the solvent is typically present in the larger quantity in a solution.

Question. d. The pressure exerted by air is called atmospheric pressure.
Answer: True
In simple words: Atmospheric pressure is the force exerted by the weight of the air molecules in the Earth's atmosphere on a surface.

🎯 Exam Tip: This is a direct definition; ensure you understand that atmospheric pressure is caused by the weight of the air column above a point.

6. Explain The Picture In Your Own Words.

Question. a. Explain the picture in your own words.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): चित्र (a) में एक दरार में पानी भरा हुआ दिखाया गया है। चित्र (b) में वही पानी तापमान कम होने पर बर्फ बन जाता है और फैलता है, जिससे दरार बड़ी हो जाती है।
• Diagram (a): Water is filled in the crack.
• Diagram (b): Water in the crack turns to ice due to decrease in temperature. When it turns to ice the volume increases and it expands. Due to expansion, the size of crack widens more than in diagram (a).
In simple words: The diagram illustrates the anomalous expansion of water, showing how water in a crack (a) turns into ice (b), expands significantly, and widens the crack due to its increased volume when frozen.

🎯 Exam Tip: Use precise terms like "anomalous expansion" and explain the cause (decrease in temperature) and effect (increase in volume, widening of crack) clearly.

7. Write Answers To The Following Questions In Your Own Words.

Question. a. How is light scattered by the air?
Answer: Air is a mixture of very fine particles of some gases, dust, smoke and moisture. When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light.
In simple words: Light is scattered by air when its rays hit tiny particles like gas molecules, dust, and water vapor, causing the light to spread out in various directions.

🎯 Exam Tip: Remember that scattering of light in air is caused by its interaction with minute particles, leading to phenomena like the blue sky.

Question. b. Explain the various properties of water.
Answer: Various properties of water are as follows:
1. It is a fluid substance because it can flow.
2. It does not have its own shape, it takes the shape of a container in which it is kept.
3. It has a definite volume.
4. It is a transparent liquid and it has no colour.
5. It is tasteless and odourless.
6. It is a universal solvent.
In simple words: Water is a fluid with definite volume but no fixed shape, it is transparent, tasteless, odorless, and famously acts as a universal solvent.

🎯 Exam Tip: List at least 4-5 distinct properties of water, focusing on its physical state, appearance, taste, smell, and solvent capabilities.

Question. c. Why is the density of seawater is more than that of rainwater?
Answer: Seawater has many minerals dissolved in it as compared to rainwater. So due to more dissolved salts, density of seawater is more than that of rainwater.
In simple words: Seawater is denser than rainwater because it contains a higher concentration of dissolved salts and minerals, which add mass to the water.

🎯 Exam Tip: The key here is dissolved salts and minerals; greater dissolved content increases mass per unit volume, hence higher density.

Question. d. What is the importance of good soil structure?
Answer: The fertility of soil depends upon soil structure. So importance of good soil structure is as follows: (a) Roots get sufficient supply of oxygen, (b) Water drainage is good therefore the roots of plants grow well.
In simple words: Good soil structure is vital for fertility as it ensures roots receive adequate oxygen and allows for proper water drainage, both crucial for healthy plant growth.

🎯 Exam Tip: Focus on how good soil structure benefits plant roots (oxygen supply) and water management (drainage) to explain its importance for fertility.

Question. e. What are the various uses of soil?
Answer: The uses of soil are as follows: Plant conservation: To help plants grow. Water conservation: Soil holds water. As a result, by means of bunds and lakes, we can get water for use throughout the year. Plasticity: (a) Soil can be given any required shape. This property of soil is called plasticity, (b) Because of its plasticity, we can use it to make articles of a variety of shapes, (c) These articles can be baked to make them hard, (d) Water storage earthen pots, earthen lamps, idols, bricks etc. are articles made from soil.
In simple words: Soil is crucial for plant growth, water conservation, and its plasticity allows it to be molded into various useful articles like pottery and bricks.

🎯 Exam Tip: Categorize the uses of soil into biological (plant growth), hydrological (water retention), and industrial/craft (plasticity for making objects) for a comprehensive answer.

Question. f. What is the need and importance of soil testing from the point of view of farmers?
Answer: 1. The properties of the various ingredients of soil can be determined by soil testing. 2. During soil testing, the soil is examined for colour, texture and the proportion of organic matter in it. 3. Soil is tested to find out if there is a deficiency of any ingredients and to decide what measures should be taken to remove the deficiency. These information would enable the farmers to maintain the fertility of the soil.
In simple words: Soil testing is crucial for farmers as it reveals soil properties, identifies nutrient deficiencies, and guides appropriate measures to maintain or improve soil fertility for better crop yields.

🎯 Exam Tip: Emphasize soil testing's role in diagnosing nutrient levels, informing corrective actions, and ultimately boosting crop productivity for farmers.

Question. g. What is the importance of air in transmission of sound?
Answer: 1. Air is useful as a medium for the transmission of sound. Density of the air changes with temperature. 2. If the density of air increases, we can hear the sound more loud and clear.
In simple words: Air acts as a medium that carries sound waves, and its density, which varies with temperature, influences how loudly and clearly we hear sounds.

🎯 Exam Tip: Highlight air as the primary medium for sound transmission and explain how its density (affected by temperature) impacts sound clarity and loudness.

Question. h. Why should a glass bottle completely filled with water never be kept in a freezer?
Answer: 1. Due to anomalous behaviour of water, when you cool water below 4°C, the volume of the water increases. 2. Therefore when the glass bottle completely filled with water is kept in a freezer, water expands on cooling and its volume increases so glass bottle breaks. 3. To avoid this, completely filled bottle is never kept in a freezer.
In simple words: A completely filled glass bottle should not be frozen because water exhibits anomalous expansion below 4°C, meaning it increases in volume when turning to ice, which can cause the bottle to shatter.

🎯 Exam Tip: The key concept is the "anomalous behavior of water"; explain that water expands upon freezing, leading to increased pressure that can break the glass container.

Project:

Question. a. Visit a soil testing laboratory. Learn the process of soil testing and share it with others.
Answer:
In simple words: Visiting a soil testing lab helps understand how soil is analyzed for its health and nutrient content, providing practical insights to share with others.

🎯 Exam Tip: This question is project-based; demonstrate understanding by outlining the purpose of a soil lab visit and the educational value of sharing findings.

Fill In The Blanks With The Appropriate Term.

Question 1. Air is a ................ of gases.
Answer: mixture
In simple words: Air is a blend of various gases, such as nitrogen, oxygen, and carbon dioxide.

🎯 Exam Tip: Remember that air is a physical mixture, not a chemical compound, of its gaseous components.

Question 2. Atmospheric pressure is the ............... in all the directions.
Answer: same
In simple words: Atmospheric pressure acts equally in all directions, pressing on surfaces from every angle.

🎯 Exam Tip: Understand that atmospheric pressure is isotropic, meaning it applies force uniformly in all directions at a given point.

Question 3. ............... is used to measure atmospheric pressure.
Answer: Barometer
In simple words: A barometer is the scientific instrument specifically designed to measure atmospheric pressure.

🎯 Exam Tip: Correctly identifying the instrument used for measuring atmospheric pressure is a direct recall question.

Question 4. As we go higher the sea level and the atmospheric pressure ............... .
Answer: decreases
In simple words: As altitude increases, there's less air above pushing down, causing atmospheric pressure to decrease.

🎯 Exam Tip: Remember the inverse relationship: higher altitude means lower atmospheric pressure due to a thinner air column.

Question 5. Pressure of air ............... when its velocity ............... .
Answer: increases, decreases
In simple words: According to Bernoulli's principle, if air velocity increases, its pressure decreases, and vice-versa.

🎯 Exam Tip: This question refers to Bernoulli's principle; state the inverse relationship between air velocity and pressure accurately.

Question 6. ............... an effect of the difference in air pressure.
Answer: Wind
In simple words: Wind is the movement of air from areas of high pressure to areas of low pressure.

🎯 Exam Tip: Connect wind directly to pressure differences; air flows to equalize pressure, creating wind.

Question 7. The level of ............... in the air is determined by its capacity to hold water vapour.
Answer: humidity
In simple words: The amount of moisture in the air, or humidity, is directly related to how much water vapor the air can hold.

🎯 Exam Tip: Define humidity as the amount of water vapor in the air, directly tied to the air's capacity to hold moisture at a given temperature.

Question 8. When the temperature of air is low, its capacity to hold the vapour is ............... .
Answer: less
In simple words: Colder air has a reduced ability to hold water vapor compared to warmer air.

🎯 Exam Tip: Understand that colder air molecules are less energetic, making them less capable of holding water vapor, leading to lower humidity capacity.

Question 9. Air is useful as a ............... for the transmission of sound.
Answer: medium
In simple words: Air serves as the medium through which sound waves travel from their source to our ears.

🎯 Exam Tip: Recognize that sound needs a medium (like air, water, or solids) to propagate; it cannot travel in a vacuum.

Question 10. Water is a ............... substance.
Answer: fluid
In simple words: Water is a fluid because it can flow and take the shape of its container.

🎯 Exam Tip: Classify water as a fluid, distinguishing it from solids by its ability to flow and conform to container shapes.

Question 11. Ice is ............... than water.
Answer: lighter
In simple words: Ice is lighter than an equal volume of liquid water because it expands and becomes less dense when it freezes.

🎯 Exam Tip: The crucial point is that ice is less dense than water, which is why it floats, a direct consequence of its anomalous expansion.

Question 12. Density of ice is ............... than that of water.
Answer: less
In simple words: The density of ice is lower than that of liquid water, explaining why ice floats.

🎯 Exam Tip: Directly connect the lower density of ice to its ability to float on water; this is a fundamental concept of water's properties.

Question 13. The space occupied by a substance is its ............... .
Answer: volume
In simple words: Volume is the amount of three-dimensional space that a substance or object occupies.

🎯 Exam Tip: Understand volume as a measure of the space an object or substance fills, a key physical property.

Question 14. The storage of matter in a substance is its ............... .
Answer: mass
In simple words: Mass refers to the amount of matter an object contains, a fundamental property distinct from weight or volume.

🎯 Exam Tip: Differentiate mass from other properties; it's a measure of the amount of substance present, reflecting its inertia.

Question 15. The density of water is maximum at ............... °C.
Answer: 4°C
In simple words: Water reaches its highest density at 4°C, after which it starts expanding as it cools further towards freezing.

🎯 Exam Tip: Remember 4°C as the specific temperature where water exhibits its maximum density, a critical point for its anomalous behavior.

Question 16. The substance in which the solute dissolves is called ............... .
Answer: solvent
In simple words: The substance that dissolves another substance is known as the solvent.

🎯 Exam Tip: Be clear on the definitions of solute (what is dissolved) and solvent (what does the dissolving).

Question 17. The particles of sandy soil are made of the mineral called ............... .
Answer: silicon dioxide (quartz)
In simple words: Sandy soil primarily consists of particles composed of silicon dioxide, also known as quartz.

🎯 Exam Tip: Identify silicon dioxide (quartz) as the main mineral component of sandy soil particles, contributing to its texture.

Question 18. ............... soil has a highest water holding capacity.
Answer: clay
In simple words: Clay soil has the highest water holding capacity due to its very fine particles and small pore spaces.

🎯 Exam Tip: Understand that clay soil's fine particle size and compact structure enable it to hold the most water, influencing its agricultural utility.

Question 19. ............... soil is red in colour.
Answer: Terracotta
In simple words: Terracotta soil is known for its distinctive red color, often due to iron compounds.

🎯 Exam Tip: Associate terracotta soil directly with its characteristic red color, which is a common visual identifier.

Question 20. ............... soil is used in cosmetics.
Answer: Multani
In simple words: Multani soil, also known as Fullers earth, is widely used in cosmetics for its absorbent and cleansing properties.

🎯 Exam Tip: Remember Multani soil (Fuller's earth) as a natural ingredient commonly found in cosmetic products for skin care.

Question 21. ............... is celebrated as World Soil Day.
Answer: 5th December
In simple words: December 5th is designated as World Soil Day to raise awareness about the importance of healthy soil.

🎯 Exam Tip: Recall the specific date, December 5th, as World Soil Day, an initiative to highlight soil conservation.

Question 22. The excess of water vapour during the night or dawn is transformed into ............... .
Answer: dew
In simple words: As temperatures drop at night, excess water vapor condenses into tiny droplets on surfaces, forming dew.

🎯 Exam Tip: Understand dew as the condensation of water vapor near the ground surface when the air cools to its dew point, often visible in the morning.

Question 23. Under ordinary conditions atmospheric pressure at sea level is ............... Newtons per square mater.
Answer: 101400
In simple words: Standard atmospheric pressure at sea level is approximately 101,400 Newtons per square meter.

🎯 Exam Tip: This is a factual recall; remember the approximate value of atmospheric pressure at sea level in N/m\(^2\).

Question 24. Swedish Scientist ............... put forth the important principle that the pressure of air decreases when its velocity increases.
Answer: Daniel Bernoulli
In simple words: Daniel Bernoulli formulated the principle that describes the inverse relationship between air pressure and velocity.

🎯 Exam Tip: Associate Daniel Bernoulli with the principle explaining the inverse relationship between fluid speed and pressure.

Question 25. When rays of light fall on fine particles of air, the particles spread light in all the directions, this is called ............... of light.
Answer: Scattering
In simple words: When light interacts with small particles in the air and spreads in all directions, this phenomenon is known as the scattering of light.

🎯 Exam Tip: Define scattering of light as the process where light rays deviate from a straight path after hitting particles, distributing the light in multiple directions.

Question 26. ............... soil is easy to plough but less fertile.
Answer: Sandy
In simple words: Sandy soil is easy to cultivate because of its loose texture, but it is less fertile due to poor nutrient and water retention.

🎯 Exam Tip: Remember that sandy soil's ease of ploughing is offset by its lower fertility, mainly due to rapid drainage and low nutrient-holding capacity.

Say Whether True Or False, Correct And Rewrite The False Statements.

Question 1. Terracotta soil is white in colour.
Answer: False. Terracotta soil is red in colour
In simple words: Terracotta soil is actually red, not white, a color derived from its iron content.

🎯 Exam Tip: Always correct false statements by providing the accurate information, in this case, the correct color of terracotta soil.

Question 2. The fertility of soil depends upon soil structure.
Answer: True
In simple words: Soil structure significantly influences its fertility by affecting water retention, aeration, and root penetration.

🎯 Exam Tip: Understand that good soil structure is critical for healthy plant growth as it supports proper air and water circulation within the soil.

Question 3. Multani soil is used to make statues and idols.
Answer: False. Shadu soil is used to make statues and idols
In simple words: Shadu soil, known for its fine texture and pliability, is actually used for making statues and idols, not Multani soil.

🎯 Exam Tip: Distinguish between different types of soil based on their specific uses; Shadu soil is known for sculpting, while Multani soil is for cosmetics.

Question 4. Clay soil has the maximum proportion of small particles.
Answer: True
In simple words: Clay soil is characterized by having the largest percentage of very fine particles, giving it a dense texture.

🎯 Exam Tip: Remember that particle size is a key differentiator for soil types; clay has the smallest particles, leading to its unique properties.

Question 5. Silt soil is not as ploughable as sandy soil.
Answer: True
In simple words: Silt soil, with its medium-sized particles, is harder to plough than sandy soil but easier than clay soil.

🎯 Exam Tip: Compare the ploughability of soil types: sandy is easiest, clay is hardest, and silt falls in between due to particle size differences.

Question 6. The colour of soil near land surface is darker than the colour of the lower layers.
Answer: True
In simple words: Topsoil is generally darker because it contains more organic matter, which decomposes and enriches the surface layers.

🎯 Exam Tip: Relate the darker color of topsoil to its higher organic content (humus), which is concentrated near the surface.

Question 7. Kerosene is a universal solvent.
Answer: False. Water is an universal solvent
In simple words: Water, not kerosene, is considered the universal solvent due to its unique ability to dissolve a wide array of substances.

🎯 Exam Tip: Correctly identify water as the universal solvent; kerosene is a non-polar solvent, effective for grease but not for many polar substances.

Question 8. The density of substance is the inter-relation between the volume and mass of a substance.
Answer: True
In simple words: Density is defined as the mass of a substance per unit volume, establishing a direct relationship between these two properties.

🎯 Exam Tip: Understand the formula for density (mass/volume) and its conceptual meaning as a measure of how much matter is packed into a given space.

Question 9. Water is lighter than ice.
Answer: False. Ice is lighter than water
In simple words: Ice is actually lighter than an equal volume of water, which is why it floats.

🎯 Exam Tip: Reiterate that ice is less dense (and thus lighter) than liquid water due to its expanded crystalline structure.

Question 10. Rotation of crops decreases the fertility of the soil.
Answer: False. Rotation of crop increases the fertility of the soil.
In simple words: Crop rotation actually boosts soil fertility by preventing nutrient depletion and improving soil health.

🎯 Exam Tip: Explain that crop rotation is a beneficial agricultural practice that enhances soil fertility by varying nutrient demands and breaking pest cycles.

Match The Columns:

Question 1.

Answer:

In simple words: The concept of pH was introduced by Sorensen; acidic soil has a pH below 6.5, neutral soil is between 6.5 and 7.5, and alkaline soil has a pH above 7.5.

🎯 Exam Tip: Match each pH range with its corresponding soil type (acidic, neutral, alkaline) and remember Sorensen as the originator of the pH scale concept.

Write Short Answers.

Question 1. What is atmospheric pressure?
Answer: The molecules of the gases in the air are in constant motion. When these molecules strike a body, they create pressure on that body. This pressure of air is called atmospheric pressure.
In simple words: Atmospheric pressure is the force exerted by the constantly moving gas molecules in the air as they collide with a surface.

🎯 Exam Tip: Define atmospheric pressure in terms of the force exerted by air molecules due to their constant motion and collisions.

Question 2. What is Bernoulli's principle?
Answer: Bernoulli's principle is that the pressure of air decreases when its velocity increases while the pressure of air increases when its velocity decreases.
In simple words: Bernoulli's principle states that for a fluid in motion, an increase in its speed corresponds to a decrease in its pressure, and vice versa.

🎯 Exam Tip: Clearly state the inverse relationship between fluid (air) velocity and pressure, as described by Bernoulli's principle.

Give Scientific Reasons.

Question 1. When the piston of a syringe is released, it is immediately pushed in.
Answer: 1. On pulling the piston of a syringe with the inlet hole of the syringe closed, more space becomes available to the air in the syringe, and it becomes rarefied.

Question 2. Water droplets are seen on the outer surface of a glass having ice cubes in it.
Answer: 1. Due to the ice cubes in the glass, the air surrounding the glass cools down. 2. As the water vapour in this air cools down, it condenses and gets transformed into water. 3. It is this water that collects on the outer surface of the glass.
In simple words: Cold ice in a glass chills the surrounding air, causing water vapor in the air to condense into tiny liquid droplets on the glass's surface.

🎯 Exam Tip: Understanding condensation is key here; relate temperature drop to water vapor changing state.

Question 3. Early morning dew drops are found on the grass.
Answer: 1. During the dawn (early morning) when the temperature of air is low, its capacity to hold the vapour is less. 2. At such times, the excess vapour is transformed into water droplets and we call them as dew drops.
In simple words: In the early morning, air cools down, reducing its ability to hold moisture. This excess moisture then condenses into small water droplets, forming dew on surfaces like grass.

🎯 Exam Tip: Focus on the relationship between air temperature and its moisture-holding capacity to explain dew formation.

Question 4. During the afternoon we feel that the air is dry.
Answer: 1. In the afternoon, when the temperature of the air is high, the capacity of the air to hold the moisture also increases. 2. Then, compared to its full capacity to hold water the proportion of moisture in the air is less and we feel that the air is dry.
In simple words: In the afternoon, higher temperatures allow the air to hold more moisture. Even if the absolute amount of moisture hasn't changed much, the air feels drier because its capacity for moisture has increased, making the existing moisture level feel relatively low.

🎯 Exam Tip: The concept of relative humidity is crucial here; emphasize how temperature affects air's moisture capacity.

Question 5. Earth's surface remains warm and suitable for the living world on the earth.
Answer: 1. The earth receives energy from the sun. This energy is reflected by the earth in the form of heat. 2. The constituents of air surrounding the earth, such as water vapour, carbon dioxide, absorb a part of this heat and give it to the other constituents of air. 3. So the Earth's surface remains warm and suitable for the living world on the earth.
In simple words: Earth absorbs solar energy and radiates it as heat. Atmospheric gases like water vapor and carbon dioxide trap some of this heat, keeping the planet warm enough to support life.

🎯 Exam Tip: This question relates to the greenhouse effect; highlight the role of atmospheric gases in retaining heat.

Question 6. We can hear the whistle of a distant train clearly early in the morning in winter.
Answer: 1. The density of air changes due to change in its temperature. 2. In winter, temperature is low so the density of the air is more. So we can hear the whistle of a distant train clearly early in the morning in winter.
In simple words: In cold winter mornings, the air is denser, which allows sound waves to travel more efficiently and with less loss, making distant sounds like a train whistle clearer.

🎯 Exam Tip: Connect air density and temperature to sound propagation speed and clarity for a complete answer.

Question 7. Ice floats on water.
Answer: 1. When water freezes means it transforms into the soild state therefore its volume increases. 2. When volume increases its density decreases 3. Therefore, density of ice is less than the water, so ice floats on water.
In simple words: Unlike most substances, water expands when it freezes, making ice less dense than liquid water. This lower density is why ice floats.

🎯 Exam Tip: The anomalous expansion of water is the key concept; remember that decreased density due to increased volume causes floating.

Question 8. In cold countries aquatic animals remain alive even after the rivers or lakes freeze in water.
Answer: 1. Due to anomalous behaviour of water, in cold countries when water gets cool and turn to ice, its volume increases, so its density decreases 2. Due to less density ice floats on water. 3. (a) Ice is a bad conductor of heat and electricity, (b) It doesn't allow outside heat to go from the ice to water so water temperature below the ice doesn't change, (c) It remains as water so aquatic animals remain alive even after the rivers or lakes freeze in winter.
In simple words: Water's unique property causes it to expand and become less dense when it freezes, so ice floats on top. This floating ice acts as an insulating layer, preventing the water below from freezing completely and allowing aquatic life to survive.

🎯 Exam Tip: Two main points: anomalous expansion of water (ice floats) and ice acting as a thermal insulator are crucial for this explanation.

Question 9. It is easier to swim in the sea than in a well or a lake.
Answer: 1. Sea water is saline. It contains salt whereas it is not so in well or a lake water. 2. Due to salts dissolved in sea water, density of sea water is more, so the swijnmer will not sink. 3. Hence, it is easier to swim in the sea than in a well or a lake.
In simple words: Seawater contains dissolved salts, making it denser than fresh water found in wells or lakes. This higher density provides more buoyancy, making it easier for a swimmer to float and move.

🎯 Exam Tip: The concept of density and buoyancy is central; explain how dissolved salts increase water's density.

Question 10. Sandy soil is less fertile.
Answer: 1. Sandy soil is made up of large particles and these particles of sandy soil are made of the mineral called silicon dioxide. 2. These particles do not dissolve in water therefore soil has very little capacity to supply nutrients, so sandy soil is less fertile.
In simple words: Sandy soil has large particles made of silicon dioxide that don't dissolve in water, which means it has a poor capacity to hold water and essential nutrients, making it less fertile for plant growth.

🎯 Exam Tip: Focus on particle size and composition impacting water and nutrient retention for soil fertility.

Question 11. China clay is used for making crockery.
Answer: China clay is used for making crockery because on heating, this clay acquires a glaze and hardness. It can be moulded into any shape and being a bad conductor of heat, it is easy to handle.
In simple words: China clay is ideal for crockery because it can be easily molded into various shapes and, when heated, develops a hard, glazed surface, and it's also a poor conductor of heat, making finished products safe to handle.

🎯 Exam Tip: Key properties are moldability, glaze/hardness after heating, and low thermal conductivity.

Answer The Following:

Question 1. Write the properties of air.
Answer: 1. Air is a mixture of gases. 2. Air has mass and volume. 3. It spreads in all directions. 4. It exerts pressure.
In simple words: Air is a mixture of various gases, it occupies space and has weight, spreads uniformly everywhere, and applies pressure on objects.

🎯 Exam Tip: Remember the fundamental physical properties of air: composition, presence of mass/volume, and pressure exertion.

Question 2. Name the tests for finding out the characteristic of soil. Describe any one method of it.
Answer: There are two tests for finding out the characteristics of soil: (1) pH (2) electrical conductivity tests. 1. pH tests: The Danish scientist Sorensen put forth the concept of pH, based on the concentration of hydrogen ions. To determine the pH of soil, a mixture of water and soil in the proportion of 1 : 2 is taken and tested using several indicators. Accordingly, soil may be found to be one of the following types.
• Acidic soil - pH less than 6.5
• Neutral soil - pH 6.5 - 7.5
• Alkaline soil - pH higher than 7.5 2. By Electrical conductivity tests we come to know how many nutrients are present in the soil.
In simple words: Soil characteristics are mainly found using pH and electrical conductivity tests. The pH test, developed by Sorensen, measures soil acidity or alkalinity based on hydrogen ion concentration, categorized as acidic (below 6.5), neutral (6.5-7.5), or alkaline (above 7.5), while electrical conductivity indicates nutrient levels.

🎯 Exam Tip: Understand both pH and electrical conductivity tests. For pH, know the range classifications (acidic, neutral, alkaline) and the role of Sorensen.

Question 3. Write the causes of diminished soil fertility.
Answer: Following are the causes of diminished soil fertility. 1. Soil pH less than 6 or higher than 8. 2. Low proportion of organic matter. 3. No proper drainage of water. 4. Repeated cultivation of the same crop. 5. Continuous use of saline water. 6. Excessive use of chemical fertilizers and pesticides.
In simple words: Soil fertility decreases due to unbalanced pH (too acidic or alkaline), low organic matter, poor water drainage, continuously growing the same crop, using saline water, and over-reliance on chemical fertilizers and pesticides.

🎯 Exam Tip: Categorize the causes into chemical (pH, fertilizers), organic (organic matter), physical (drainage), and agricultural practices (crop rotation, saline water) for easy recall.

Question 4. Which crops reduce the fertility of soil and Which crops increase the fertility of soil?
Answer: Wheat reduces the fertility of soil and leguminous crops like peanut, moong, moth bean, pea, lentil, Bengal gram, soyabean increase the fertility of soil.
In simple words: Crops like wheat deplete soil fertility, whereas leguminous crops such as peanut, moong, moth bean, pea, lentil, Bengal gram, and soybean enrich the soil by fixing nitrogen.

🎯 Exam Tip: Remember that leguminous plants are key for increasing soil fertility due to their nitrogen-fixing capabilities, while heavy feeders like wheat can deplete it.

Question 5. Name and explain some useful types of soil.
Answer: Following are some useful types of soil. 1. China clay (Kaolin): (a) It is white in colour, (b) It is used to make crockery, bathroom tiles, tanks, laboratory apparatus, masks, jars etc. 2. Shadu soil: (a) It is whitish in colour, (b) It is used for making statues and idols. 3. Terracotta soil: (a) This soil is red in colour, (b) Decorative articles and pots used for growing plants are made from this soil. 4. Multani soil: This soil is used in cosmetics.
In simple words: Useful soil types include China clay (white, used for ceramics and labware), Shadu soil (whitish, for statues), Terracotta soil (red, for decorative pots), and Multani soil (used in cosmetics).

🎯 Exam Tip: For each soil type, remember its key characteristic (color) and its primary use.

Question 6. Explain the types of soil on the basis of its texture.
Answer: There are 3 types of soil on the basis of its texture. 1. Sandy soil: (a) Large particles are high in sandy soil, (b) Water drains rapidly through sandy soil, (c) It is easy to plough this soil, (d) It is less fertile because the particles of sandy soil are made of the mineral called silicon dioxide (quartz), (e) These particles do not dissolve in water and therefore the soil has very little capacity to supply dissolved nutrients. 2. Silt soil: (a) The particles of silt soil are of medium size, (b) Silt soil is not as ploughable as sandy soil but is much more ploughable than clay soil, (c) This soil contains a large proportion of organic materials, (d) Its capacity to supply nutrients is much greater, (e) Silt soil is also called sedimentary soil. 3. Clay soil: (a) The proportion of small particles is maximum, (b) The particles of clay soil feel smooth to touch, (c) Clay soil has a high water holding capacity.
In simple words: Soils are classified by texture into sandy (large particles, poor water/nutrient retention, easy to plough), silt (medium particles, good organic content and nutrient supply, moderate ploughability), and clay (finest particles, smooth, high water holding capacity).

🎯 Exam Tip: For each soil type, relate particle size to its properties like water drainage, nutrient retention, and ease of ploughing.

Explain The Given Picture In Your Own Words.

Question 1.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र जल में आलू के घनत्व के व्यवहार को दर्शाता है। चित्र (a) में आलू को सामान्य पानी में डुबोया गया है, जहां वह डूब जाता है क्योंकि उसका घनत्व पानी से अधिक है। चित्र (b) में आलू को नमक के घोल में रखा गया है, जहां वह तैरता है क्योंकि नमक मिलाने से घोल का घनत्व बढ़ जाता है, जो आलू के घनत्व से अधिक हो जाता है।
Answer: 1. The potato will sink in water as potato's density is more than water. 2. This is the effect of density. The potato will float in salt solution as the density of salt solution is more than potato. The density of the water becomes greater due to the dissolved salt. That is why it is easier to swim in sea than in a well or a lake.
In simple words: A potato sinks in plain water because it's denser, but floats in salt solution because the added salt increases the water's density, making it greater than the potato's, illustrating how density affects buoyancy.

🎯 Exam Tip: Relate the potato's behavior to the density of the liquid; higher liquid density (due to salt) increases buoyancy.

Can You Tell?

Answer The Following Questions.

Question 1. What change takes place in a balloon on filling air in it?
Answer: On filling air in balloon, the shape of the balloon changes. Its size increases due to expansion.
In simple words: When air is blown into a balloon, it inflates, changing its shape and increasing its size as the air expands to fill the space.

🎯 Exam Tip: Focus on the physical changes: change in shape, increase in size, and the underlying reason of expansion.

Question 2. Why is it easier to swim in the sea than in a well or a lake?
Answer: 1. Sea water is salty due to minerals in it. Whereas it is absent in well or a lake water. 2. Due to presence of salts, density of seawater is more than well or lake water, so it is easier to swim in the sea than in a well or lake.
In simple words: Swimming is easier in the sea because its salt content makes the water denser than fresh water in wells or lakes, providing more upward buoyant force.

🎯 Exam Tip: The core concept is that dissolved salts increase seawater's density, leading to greater buoyancy.

Use Your Brain Power!

Answer The Following Questions.

Question 1. What is the effect of increased temperature on the pressure of air?
Answer: Condition for closed environment: 1. When the temperature increases, the pressure of air also increases. 2. For example, as the air warms up, the molecules in the air become more active. 3. They use up more individual space even though there is same number of molecules. T1 s causes an increase in the air pressure.
In simple words: In a closed space, increasing the temperature of air makes its molecules move faster and collide more frequently and forcefully with the container walls, leading to an increase in air pressure.

🎯 Exam Tip: Connect increased temperature to increased molecular kinetic energy and collision frequency, which directly relates to pressure.

Question 2. Dip an uncorked inverted empty bottle in a slanting position into the water in a wide container. What do you observe?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र दर्शाता है कि खाली बोतल वास्तव में हवा से भरी होती है। जब एक उल्टी बोतल को तिरछा करके पानी में डुबोया जाता है, तो बोतल के अंदर फंसी हवा बुलबुले के रूप में बाहर निकलती है, और उसका स्थान पानी ले लेता है, जिससे यह सिद्ध होता है कि हवा स्थान घेरती है।
Answer: 1. When an uncorked inverted empty bottle is kept slanting in the water container bubbling sound will be heard. 2. Air bubbles come out from the empty bottle and water enters the bottle. 3. Empty bottle is actually not empty but it is occupied by air. 4. When this air comes out, its place is taken by water. This shows that air occupies space.
In simple words: When an inverted "empty" bottle is dipped slantwise into water, bubbling occurs as the trapped air escapes, allowing water to enter. This demonstrates that air occupies space, proving the bottle wasn't truly empty.

🎯 Exam Tip: This experiment visually confirms that air has volume and occupies space, a fundamental property of matter.

Question 3. In cold countries how do aquatic animals remain alive even after the rivers or lakes freeze in winter.
Answer: 1. Due to anomalous behaviour of water, in cold countries, water changes to ice. 2. Due to this change, its volume increases and density decreases. So ice floats on water. 3. Ice is a bad conductor of heat so it doesn't allow heat to go inside so the water below ice remains as it is. So aquatic animals remain alive even after the rivers or lakes freeze in winter.
In simple words: In cold regions, water's anomalous expansion means ice floats and acts as an insulator, preventing the water beneath it from freezing solid. This allows aquatic animals to survive in the liquid water layer below the ice.

🎯 Exam Tip: Emphasize both the anomalous expansion (ice floats) and the insulating property of ice as crucial for aquatic survival in freezing conditions.

Question 4. Why is it difficult to plough clay soil?
Answer: It is difficult to plough clay soil because in clay soil the proportion of small particles is maximum. The particles of clay soil feel smooth to touch and has high water holding capacity, making it very difficult to penetrate through it.
In simple words: Clay soil is hard to plough because it consists of very fine particles that pack tightly and retain a lot of water, making it dense and resistant to penetration.

🎯 Exam Tip: Focus on the small particle size and high water retention of clay soil as the main reasons for its difficulty in ploughing.

Question 5. Why is it easy to plough sandy soil?
Answer: 1. Sandy soil has large sized particles. It has weak structure due to less organic matter and large spaces between them. 2. The water also drains quickly through it making it dry and allows the plough to penetrate through it.
In simple words: Sandy soil is easy to plough because its large particles create a loose structure with ample air spaces, allowing water to drain quickly and offering little resistance to farm implements.

🎯 Exam Tip: Contrast with clay soil by highlighting large particle size, weak structure, and rapid drainage as factors for easy ploughing.

Question 6. What is the water holding capacity of silt soil?
Answer: Silt occurs as a deposit in riverbeds. The size of silt particles is between those of sand and clay. This soil also has humus in it which makes it the best soil to hold the right amount of water.
In simple words: Silt soil, found in riverbeds, has medium-sized particles, and with its humus content, it possesses an optimal water-holding capacity, making it excellent for agriculture.

🎯 Exam Tip: Note the intermediate particle size and the presence of humus as key factors contributing to silt soil's good water retention.

Question 7. Which soil is suitable for cultivation? Why?
Answer: The silt soil is suitable for cultivation. 1. The particles of silt soil is of medium size. 2. Silt soil is much more ploughable than clayey soil. 3. It contains large proportions of organic material. 4. This helps the soil in retention of water for a proper amount of time and makes it suitable for crops to grow.
In simple words: Silt soil is best for cultivation because its medium particle size, good ploughability, rich organic matter content, and balanced water retention create ideal conditions for healthy crop growth.

🎯 Exam Tip: Combine the advantages of silt soil (particle size, organic matter, water retention) to explain its suitability for cultivation.