Text Book Solutions All Class

Short Questions and Answers

Q1: Define heat.
Ans: Heat is a form of energy which produces a sensation of warmth and flows when there is a temperature difference between two bodies.  It is measured in joules or calories.

Q2: Define temperature. What is its unit?
Ans:  A reliable measure of the hotness of an object is its temperature. Temperature is measured by a device called a thermometer. The unit of temperature is degree Celsius (°C), Fahrenheit, and Kelvin (SI unit).

Q3: What is the use of the maximum-minimum thermometer?
Ans: The maximum-minimum thermometer is used to measure the highest and lowest temperatures of a place in a day. It is commonly used in weather stations to track daily temperature variations. This thermometer helps in understanding temperature fluctuations, which is essential for weather forecasting and analysis.

Max-min Thermometer

Q4: : What is conduction?
Ans: Heat flows from a hotter object to a colder object. The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

Q5: Why conduction is only possible in solids?
Ans: In solids, generally, the heat is transferred by the process of conduction because particles of solids are closely packed, and heat is transferred from the hotter end to the colder end of an object.

Q6: How does the heat from the sun reach us?
Ans:  Heat from the sun reaches us by radiation, which does not require a medium to transfer heat. Unlike conduction (which occurs in solids) and convection (which occurs in liquids and gases), radiation can transfer heat even through the vacuum of space

Q7: Explain how water is heated by convection.

Ans: The water is a poor conductor of heat, so do not heat it by conduction. When water is heated, the water becomes lighter. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises upward, and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection.

Q8: Differentiate between conductor and insulators?
Ans: The materials which allow heat to pass through them easily are conductors of heat. For example, aluminum, iron, and copper The materials that do not allow heat to pass through them easily are poor conductors of heat, known as insulators, such as plastic and wood.

Q9: Explain land breeze.
Ans: The water cools down more slowly at night than the land. So, the cool air from the land moves towards the sea. This is called the land breeze.

Q10: Explain sea breeze.
Ans: During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up. The sea’s cooler air rushes towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea is called the sea breeze.

Long Questions and Answers

Q1: How does heat transfer take place in solids, liquids, and gases?
Ans: Heat can be transferred in three different ways depending on the medium:

Conduction (Solids)

• In solids, heat travels from one particle to another without movement of the particles.
• Example: A metal spoon gets hot when placed in a cup of tea.

Convection (Liquids & Gases)

• In liquids and gases, heat moves through rising hot particles and falling cold particles.
• Example: Boiling water in a pan shows upward movement of hot water and downward movement of cold water.

Radiation (Without Medium)

• Heat can also be transferred without any medium in the form of rays.
• Example: Heat from the Sun reaches Earth through space by radiation.

Thus, different materials transfer heat in different ways, and understanding these helps in designing better insulators and conductors.

Q2: State similarities between the laboratory thermometer and the clinical thermometer.

Ans: Similarities between laboratory thermometer and clinical thermometer are :

• Both are used to measure temperature.
• Both typically use mercury or digital technology to display readings.
• Both require careful handling to ensure accurate readings.
• Both thermometers have a scale marked in degrees Celsius.

Q3: Why do coastal areas experience land breeze and sea breeze?

Ans: In coastal areas, the movement of air between land and sea causes land breeze and sea breeze.

1. Sea Breeze (Daytime)
   • During the day, the land heats up faster than the sea.
   • The air above the land becomes hot and rises, while cooler air from the sea moves in to take its place.
   • This movement of air from the sea to the land is called sea breeze.
2. Land Breeze (Nighttime)
   • At night, the land cools down faster than the sea.
   • The air above the sea remains warmer and rises, and the cooler air from the land moves towards the sea.
   • This movement of air from the land to the sea is called land breeze.

These breezes help moderate temperatures in coastal areas, making them more comfortable.

Short Questions and Answers

Q1: What is adolescence?
Ans: Adolescence is the stage of growth and development between childhood and adulthood, typically occurring between the ages of 10 and 19. It involves rapid physical, emotional, and behavioral changes.

Q2: At what age does adolescence generally start?
Ans: Adolescence generally starts around the age of 10 years.

Q3: What is puberty?
Ans: Puberty is the stage in adolescence when the body undergoes external and internal changes to develop into an adult capable of reproduction.

Q4: What is the role of hormones during adolescence?
Ans: Hormones regulate various aspects of growth and development during adolescence, influencing physical, emotional, and behavioral changes.

Q5: What are secondary sexual characteristics?
Ans: Secondary sexual characteristics are traits that help distinguish males from females, like the development of breasts in girls or facial hair in boys, which mark the onset of puberty.

Q6: How does the voice change during adolescence in boys?
Ans: In adolescent boys, the voice box grows, leading to a hoarse voice. This is visible as the development of the Adam’s apple.

Q7: What is menstruation, and when does it start?
Ans: Menstruation is the process where adolescent girls experience a monthly discharge of blood from the uterus, marking the onset of reproductive capability, typically starting around the age of 12.

Q8: Why do acne and pimples appear during adolescence?
Ans: Acne and pimples appear during adolescence due to an increase in oily secretions from the skin, which can clog pores and lead to infections.

Q9: How do boys and girls differ in terms of body changes during adolescence?
Ans: Boys typically experience the development of a deeper voice, facial hair, and broader shoulders. Girls experience changes like breast development and wider hips, along with a menstrual cycle.

Q10: What is the importance of a healthy diet during adolescence?
Ans: A healthy diet is crucial during adolescence as it supports rapid growth and development, providing essential nutrients like proteins, vitamins, and minerals for optimal physical and mental health.

Long Questions and Answers

Q1: Discuss the physical changes that occur in both boys and girls during adolescence.
Ans: During adolescence, both boys and girls experience significant physical changes. Boys typically undergo growth in height, develop broader shoulders, and experience the growth of facial hair, such as moustaches and beards. Their voices become deeper due to the growth of the voice box (Adam’s apple). Girls also grow in height and experience the development of breasts and wider hips. Both boys and girls develop hair in the armpits and pubic regions. Additionally, boys may develop chest and back hair, although this is not universal. Pimples and acne are common for both genders due to increased oily secretions from the skin.

Q2: Explain the concept of puberty and its relation to reproductive health.
Ans: Puberty is a critical stage in adolescence where the body undergoes both external and internal changes that prepare it for reproduction. It marks the transition from childhood to adulthood. In girls, puberty is associated with the start of menstruation, which is a key indicator of reproductive capability. In boys, puberty involves the development of secondary sexual characteristics like facial hair and a deeper voice, signaling the body’s readiness for reproduction. Puberty involves hormonal changes that drive these physical transformations, preparing individuals for adulthood.

Q3: How do emotional and behavioral changes affect adolescents, and what steps can they take for positive growth?
Ans: Adolescents undergo significant emotional and behavioral changes due to the surge in hormones. They may experience mood swings, increased sensitivity, and curiosity, leading to both positive and negative behavior. These emotional changes can lead to stronger feelings of empathy, social engagement, and self-exploration, but may also cause confusion and impulsive decisions. To ensure positive growth, adolescents can engage in various activities like sports, music, or volunteering, which help them channel their emotions productively. Seeking guidance from trusted adults and maintaining healthy social relationships also aid in emotional stability.

Q4: What are the challenges and benefits of maintaining good hygiene during adolescence?
Ans: During adolescence, personal hygiene becomes increasingly important as the body undergoes significant changes. Good hygiene, especially in areas like the armpits, face, and pubic region, helps prevent infections and body odor. Girls, in particular, must maintain menstrual hygiene to ensure comfort and health. While maintaining hygiene can be challenging due to the increase in sweat and body changes, it is essential to prevent skin conditions like acne and other infections. Using sanitary pads during menstruation, regularly washing the face, and wearing clean clothes are simple yet effective ways to maintain hygiene and support overall health.

Q5: Discuss the risks associated with substance abuse during adolescence and how to avoid them.
Ans: Adolescence is a period marked by curiosity and peer pressure, which can make adolescents more susceptible to trying harmful substances like tobacco, alcohol, and drugs. These substances can have serious effects on physical and mental health, leading to addiction, lung damage, memory loss, and other severe health issues. It is important for adolescents to understand the risks of substance abuse and to make informed decisions. They can avoid these risks by saying “NO” to peer pressure, seeking support from family and teachers, and engaging in healthy activities like sports and hobbies. Educating adolescents about the harmful effects of substances and providing a supportive environment helps them make healthier choices.

Short Answer Questions

Q1: Explain physical reaction along with examples.
Ans : A change in which a substance undergoes a change in its physical properties is called a physical change. For example; melting of ice.
Q2: Explain chemical reaction along with examples.
Ans : A change in which one or more new substances are formed is called a chemical reaction. For example; rusting of iron.
Q3: Differentiate between physical and chemical reactions.
Ans : Physical ReactionChemical Reaction A change in the physical properties of a substance. A change in which one or more new substances are formed. A physical change is generally reversible. A chemical change is generally irreversible. 

Q4: State the condition necessary for the occurrence of any reactant.
Ans : For the occurrence of any reaction, the following condition is necessary:

• The molecules or atoms of the reactants must collide with each other.
• This collision is essential to break old bonds and form new ones.

Q5: Why new products are formed in a chemical reaction?
Ans : New products are formed in a chemical reaction due to the following reasons:

• The old bonds between atoms in the reactants are broken.
• New bonds are created, leading to the formation of different substances.
• The resulting products have different properties compared to the original reactants.

Q6: Explain the process of rusting.
Ans: The process of rusting occurs when iron is exposed to damp air or water for a long time. This results in a reddish-brown flaky substance known as rust. The key steps in rusting are:

• Iron reacts with oxygen from the air.
• This reaction requires the presence of water or moisture.
• The outcome of this reaction is a compound called iron oxide.

Rusting is accelerated in humid conditions, making it a significant issue for iron objects.

Q7: How can we prevent rusting?
Ans: To prevent rusting, it is essential to keep iron, water, and oxygen apart. Here are some effective methods:

• Apply a coat of paint or grease regularly to create a barrier.
• Use wax or oil coatings, especially for vehicles.
• Keep tools and equipment dry; wipe them down after use.
• Store items in a dry place to avoid moisture.

Q8: Setting of curd is regarded as a chemical change, explain why?
Ans: The setting of curd is considered a chemical change for the following reasons:

• The original substance, milk, cannot be recovered after curd is formed.
• Curd has distinct taste, smell, and chemical properties compared to milk.
• New substances are created during the process, indicating a transformation.

Q9: What happens when baking soda is treated with vinegar?
Ans: When baking soda is mixed with vinegar, a reaction occurs that produces a hissing sound and bubbles. This is due to the formation of carbon dioxide gas. The chemical equation for this reaction is:

• Vinegar (Acetic acid) + Baking soda (Sodium hydrogen carbonate) → Carbon dioxide + other substances.

The bubbles you see are the carbon dioxide gas being released during the reaction.

Q10: What happens when a piece of iron metal is placed in copper sulphate solution?
Ans: When iron is placed in Copper sulphate solution, the iron is coated with a brown coloured substance “copper” and CuSO₄ solution changes from blue to light green. This is due to iron displacing copper as it is more reactive than copper.

Q11: Explain the changes occuring in burning of candle.
Ans: When a candle burns, it undergoes both physical and chemical changes:

• The wax melts as it heats up, which is a physical change because it can solidify again when cooled.
• As the candle burns, it produces light and gases, such as carbon dioxide, indicating a chemical change due to the combustion of the wick.

Q12: Baking soda is mixed with lemon juice, bubbles are formed with the evolution of gas, explain the changes occurred here.
Ans: When baking soda is mixed with lemon juice, a chemical reaction occurs, resulting in the formation of bubbles. This happens because:

• A new substance, carbon dioxide, is produced during the reaction.
• The release of gas creates visible bubbles.
• This process is an example of a chemical change as new substances are formed.

Q13: Name some of the process in which both chemical and physical changes take place.
Ans: One example of a process that involves both chemical and physical changes is the burning of wood:

• The moisture in the wood turns to vapor when heated, which is a physical change.
• The actual burning produces carbon dioxide and other products, indicating a chemical change.

Q14: Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Ans: Burning of wood produces ash and smoke. Hence the properties of wood are changed and new substances are formed. So, it is a chemical reaction. When a log of wood is cut into small pieces,there is no new substance formed. Each small piece bears the properties of wood. So, its a physical change.Obviously, burning and cutting of wood are two different types of changes.

Q15: Explain how painting of an iron rod prevents it from rusting.
Ans: To prevent rusting, it is essential to stop iron from contacting both air and moisture. Painting an iron gate achieves this by:

• Creating a protective barrier that blocks air and moisture.
• Reducing the chances of rust formation.
• Ensuring the iron remains dry and free from corrosive elements.

Regular maintenance of the paint layer is important to keep the iron protected. 

Q16: A part from new products, many other things accompany a chemical change, what are those things?
Ans : Part from new products, many other things accompany a chemical change, those things are:

• Heat, light or any other radiation may be given off or absorbed.
• Change in smell may take place.
• Sound may be produced.
• Change in colour may take place.
• A gas may be formed

Q17: Burning of any substance is the chemical change. Discuss.
Ans: Burning of any substance is a chemical change. Burning involves a series of changes:

• Heat is always produced.
• The old bonds in the reactants are broken.
• New bonds are formed, leading to new products.
• The properties of these new products differ from the original substances.

Thus, burning is a clear example of a chemical change. 

Q18: State Four characteristics which are included in the physical properties of matter.
Ans: Physical properties of matter include the following characteristics:

• Shape: The form or outline of an object.
• Size: The dimensions or magnitude of an object.
• Colour: The visual perception of light reflected from an object.
• State: The physical form of matter, such as solid, liquid, or gas.

Q19: Why formation of manure from leaves is a chemical change?
Ans: The formation of manure from leaves is a chemical change because:

• It produces a new substance with a different composition.
• The original leaves undergo a transformation that alters their chemical structure.

Q20: Why cutting of wood is a physical change?
Ans: Cutting of wood is classified as a physical change for the following reasons:

• The identity of the wood remains the same.
• Its composition does not change.
• No new substances are formed during the process.

Thus, cutting wood is a reversible change that affects its shape and sizebut not its fundamental properties. 

Long Answer Questions

Q1: Explain the physical and chemical processes along with examples.
Ans: A change in which a substance undergoes a change in its physical properties is called physical change, physical properties involves shape, size, colour and state of a substance. It is generally reversible; in physical change no new substance is formed. For example: evaporation, condensation etc.
A change in which one or more new substances are formed is called chemical change. Chemical change is irreversible. It is also called chemical reaction; in this type of change a new substance is formed. Example—Burning of coal, photosynthesis.
The difference between physical change and chemical change is as follows-Physical change
(1) No new substance is formed. A substance undergoes a change in its physical properties.
(2) Physical change is generally reversible.
Example—Melting of ice, lighting of bulb Chemical Change
(1) One or more new substances are formed by chemical reaction.
(2) Chemical change is irreversible.
Example—burning of coal, photosynthesis

Q2: Explain the process of rusting of iron, and measures to prevent the same.
Ans: 

The process of rusting occurs when iron reacts with oxygen and water, forming a reddish-brown substance known as rust (iron oxide). This reaction is accelerated in humid conditions where moisture is abundant. To prevent rusting, consider the following methods:

• Galvanisation: This involves coating iron with a layer of zinc, which protects it from moisture and oxygen.
• Painting or Greasing: Applying a coat of paint or grease creates a barrier that prevents contact with air and water.
• Using Stainless Steel: Stainless steel, made by mixing iron with chromium and other metals, is resistant to rust.

Regular maintenance of protective coatings is essential to ensure long-lasting protection against rusting. 

Q3: Why chemical changes are very important in our life?
Ans: A chemical change occurs when the composition of a substance is altered, resulting in the formation of one or more new substances. This process is essential in our daily lives for several reasons:

• New substances are created through chemical changes, such as during the digestion of food and the ripening of fruits.
• Medicines are produced as a result of complex chemical reactions.
• Many useful materials, including plastics and detergents, are formed through chemical processes.
• Every new material discovered is linked to the study of chemical changes.

In summary, chemical changes are vital as they lead to the creation of essential substances and materials that support life and industry. 

Q4: Rusting of an iron object is faster is coastal areas than in desert area. Explain why?
Ans: Rusting of an iron object occurs more rapidly in coastal areas than in desert regions due to the following reasons:

• Coastal areas have higher levels of moisture in the air because of the nearby sea.
• Deserts, on the other hand, have dry air with little to no moisture.
• Both air and moisture are essential for rusting to take place.
• Thus, the increased humidity in coastal areas leads to faster rusting compared to the arid conditions of deserts.

Short Questions and Answers

Q1: What is malleability?
Ans: Malleability is the property of materials by which they can be beaten or hammered into thin sheets. Metals like copper, aluminium, and iron possess malleability.

Q2: What happens when metals like copper and aluminium are beaten with a hammer?
Ans: Metals like copper and aluminium become flattened when beaten with a hammer, demonstrating their malleability.

Q3: What is ductility?
Ans: Ductility is the property of materials that allows them to be drawn into wires. Metals such as gold and copper are highly ductile.

Q4: What is sonority in metals?
Ans: Sonority is the property of metals to produce a ringing sound when struck. Metals like iron and steel are sonorous.

Q5: Why are metals used for cooking utensils?
Ans: Metals are good conductors of heat, which makes them ideal for cooking utensils as they quickly transfer heat to food.

Q6: What is corrosion?
Ans: Corrosion is the gradual deterioration of metals due to reactions with air, water, or other substances. For example, iron rusts when exposed to moist air.

Q7: What happens when metals react with oxygen?
Ans: When metals react with oxygen, they form metal oxides, which are usually basic in nature.

Q8: Why are metals like iron and copper used in electrical wiring?
Ans: Metals like iron and copper are good conductors of electricity, making them ideal for use in electrical wiring.

Q9: Why is sodium stored in kerosene?
Ans: Sodium reacts vigorously with water and oxygen, generating a lot of heat. Storing sodium in kerosene prevents it from reacting with moisture and air.

Q10: What is the importance of metals and non-metals in everyday life?
Ans: Metals and non-metals play vital roles in daily life. Metals are used in construction, electrical devices, and tools, while non-metals like oxygen and nitrogen are essential for life and plant growth.

Long Questions and Answers:

Q1: Describe the physical properties of metals and how they differ from non-metals.
Ans: Metals generally exhibit properties like metallic lustre, malleability, ductility, sonority, and high conductivity of heat and electricity. Non-metals, on the other hand, are generally non-lustrous, brittle, and poor conductors of heat and electricity. Metals can be hammered into sheets (malleable) and drawn into wires (ductile), whereas non-metals lack these properties. Non-metals also form acidic oxides when they react with oxygen, while metals typically form basic oxides.

Q2: How does the reaction of metals and non-metals with oxygen differ?
Ans: Metals generally react with oxygen to form basic metal oxides, such as iron oxide (rust), which is alkaline in nature. Non-metals, on the other hand, form acidic oxides when they react with oxygen, such as sulfur dioxide, which forms sulfurous acid when dissolved in water. This difference in reactions is key to understanding the nature of oxides formed by metals and non-metals.

Q3: Explain the process of rusting and how it can be prevented.
Ans: Rusting is the process where iron reacts with oxygen and water to form iron oxide (rust), which causes the iron to deteriorate. Rusting can be prevented by methods such as painting, oiling, greasing, or applying a protective layer of zinc (galvanization). These methods protect the iron from direct exposure to air and water, thus preventing corrosion.

Q4: What are the applications of metals in daily life?
Ans: Metals have numerous applications in daily life due to their distinct properties. For instance, metals like copper and aluminium are used for electrical wiring due to their excellent conductivity. Iron and steel are used in construction and making tools due to their strength and malleability. Precious metals like gold and silver are used in jewelry, while aluminium is used in food packaging materials due to its malleability and low cost. Metals are also used in the manufacturing of machinery, vehicles, and electronics.

Q5: Discuss the uses of non-metals in everyday life.
Ans: Non-metals like oxygen are essential for respiration, making them crucial for life. Nitrogen is used in fertilizers to enhance plant growth. Carbon is an important element in organic molecules and fuels. Chlorine is used in water purification, while iodine is used as an antiseptic for wounds. Non-metals are also found in medicines, food preservation, and industrial applications like rubber manufacturing and water treatment.

Short Answer Questions:

Q1: What is a torchlight?
Answer: A torchlight is a portable device that produces light, commonly used to see in the dark.Torchlight

Q2: What is the function of the electric cell in a torchlight?
Answer: The electric cell provides the energy needed to make the lamp glow by allowing current to flow from the positive to the negative terminal.

Q3: How does an electric circuit work?
Answer: An electric circuit is a complete path that allows current to flow from a power source (like a cell) through a device (like a lamp) and back, making the device work.

CircuitQ4: What is the difference between an electric cell and a battery?
Answer: An electric cell is a single source of electrical energy, while a battery is a combination of two or more cells connected together to provide more energy.

Q5: What is an incandescent lamp?
Answer: An incandescent lamp has a filament inside that glows when electric current passes through it, producing light.

Q6: What is the function of a switch in a circuit?
Answer: A switch controls the flow of current by either completing (closing) or breaking (opening) the circuit.

Q7: What is the purpose of using insulators in electrical circuits?
Answer: Insulators prevent the flow of electric current and are used to cover wires and make switches and plugs to ensure safety.

Q8: What is a circuit diagram?
Answer: A circuit diagram is a drawing that uses standard symbols to represent the components of an electrical circuit.

Circuit DiagramQ9: What is the role of a filament in an incandescent lamp?
Answer: The filament inside the incandescent lamp glows when heated by the electric current, producing light.

Q10: What are the types of electricity used in devices?
Answer: The two main types of electricity are Direct Current (DC), used in devices like torchlights and phones, and Alternating Current (AC), used for larger appliances.Long Answer Questions:

Q1: Explain how an electric cell works in providing energy to a device.

Answer:  

•  An electric cell is a source of electrical energy. 
•  It has two terminals: a positive (+) terminal and a negative (-) terminal. 

Electric Cell

•  These two terminals are connected by a circuit. 
•  Inside the cell, a chemical reaction occurs between the materials inside the cell. 
•  This chemical reaction releases electrons (tiny charged particles) that move from the negative terminal to the positive terminal, creating an electric current. 
•  This current flows through the wires of the circuit and powers the devices connected to it, like lamps, radios, clocks, or remote controls. 
•  The flow of current from the electric cell provides the energy needed for these devices to work. 

Q2: Describe the structure and working of an LED lamp.

Answer: 

•  An LED lamp is different from traditional lamps like incandescent or fluorescent lamps. 
•  It does not have a filament, but instead uses a special material called a diode to produce light. 
•  The LED lamp has two terminals: one longer (positive terminal) and one shorter (negative terminal). 
•  The lamp is designed to glow when the positive terminal of the lamp is connected to the positive side of a battery or power source, and the negative terminal is connected to the negative side. 
•  When current flows through the LED, it moves in only one direction because LEDs only work when the current is going from the positive to the negative terminal. 
•  This makes LEDs more efficient, meaning they use less energy to produce light and last longer than regular bulbs. 
•  Since there is no filament, LED lamps are less likely to break or burn out, which makes them more durable. 

Q3: How does a simple electrical circuit work to make a lamp glow?

Answer: 

• A simple electrical circuit consists of a few key parts: an electric cell (like a battery), a lamp, and wires.
• When the switch in the circuit is in the “on” position, it allows electricity to flow from the positive terminal of the cell through the wires and into the lamp.
• Inside the lamp, there is a filament (a thin wire), and when electricity passes through the filament, it heats up and starts to glow.
• This produces light.
• If the switch is turned off, the circuit becomes incomplete, and the electric current cannot flow, so the lamp will not glow.
• The switch is used to either allow or stop the flow of electricity, controlling when the lamp is on or off.

Q4: What are the roles of conductors and insulators in electrical circuits?

Answer: In an electrical circuit, conductors and insulators play important roles:

Conductors vs Insulators

• Conductors are materials that allow electricity to flow through them easily. Metals like copper, silver, and aluminum are good conductors. They are used in the wires that connect different parts of an electrical circuit because they let the electric current pass through them without resistance.
• Insulators, on the other hand, are materials that do not allow electricity to flow. They protect us from electric shocks. Common insulators include plastic, rubber, and wood. These materials are used to cover wires, make electrical switches, and create plug tops. They make sure that the current stays inside the wires and does not harm us or cause short circuits.

In simple terms, conductors let electricity flow, while insulators keep electricity safely contained within the circuit.

Q5: Discuss the importance of switches in electrical circuits.

Answer: 

• A switch is an important device in electrical circuits because it helps control the flow of electricity.
• The switch acts like a gate for the electric current.
• When the switch is in the “on” position, it closes the circuit, allowing electricity to flow through and power the connected device, such as a lamp, fan, or television.
• This makes the device work.
• When the switch is in the “off” position, it opens the circuit, which stops the flow of electricity.
• As a result, the device is turned off.
• Switches are essential for turning electrical devices on and off safely and efficiently.
• Without switches, you would have to disconnect wires every time you want to turn something off, which would be impractical and unsafe.
• Therefore, switches make electrical circuits safer and easier to use, as they give us control over the devices that run on electricity.

Short Q&A:

Q1: What is litmus and how is it used to identify acids and bases?
Ans: Litmus is a natural material made from lichens and comes as blue and red paper strips. It helps identify substances: acids turn blue litmus paper red, and bases turn red litmus paper blue.

LitmusQ2: How is red rose extract prepared and how does it act as an indicator?
Ans: Red rose extract is made by crushing fresh rose petals, soaking them in hot water, and filtering the liquid. It changes color to red in acidic substances and green in basic substances, helping to identify them.

Red Rose Petas immersed in Hot WaterQ3: What color change does turmeric paper show when it comes in contact with a base?
Ans: Turmeric paper, which is yellow, turns red when it touches a basic substance. It does not change color with acidic or neutral substances.

Q4: What are olfactory indicators and give an example?
Ans: Olfactory indicators are substances whose smell changes when mixed with acids or bases. For example, a cloth soaked in onion juice loses its smell when put in acidic tamarind water or basic baking soda solution.

Q5: Name two other natural indicators besides litmus and red rose extract.
Ans: Beetroot and purple cabbage are natural indicators. They change color when mixed with acidic or basic substances.

IndicatorsQ6: Red litmus paper is dipped in a solution; it remains red, what is the nature of the solution?
Ans : Red litmus paper when dipped in a solution, if it remains red then the nature of the solution is neutral.

Q7: What are salts? Give examples.
Ans : Salts are the ionic compounds generally formed by neutralisation of an acid with base. They can be acidic, basic as well as neutral. Example acidic salts: sodium bicarbonate, basic salts: magnesium chloride, neutral salt: sodium chloride.

Q8: Give examples of some acids and bases
Ans : Curd, lemon juice, vinegar, orange juice etc. are acids and baking soda, lime water etc. are bases.

Q9: Define indicators along with examples.
Ans : Indicators are special type of substance that are used to taste whether a substance is acidic or basic in nature. It change the colour of acidic or basis substances when added into it. Turmeric, litmus, etc. are some natural indicators.

Turmeric as IndicatorQ10: What do you mean by neutral substance, explain with examples?
Ans : The substances which are neither acidic, nor basic are called neutral substance. These substances neither turn blue litmus red nor red litmus blue, for example distilled water, sugar solution etc.

Q11: Rena is trying to wash turmeric stain on her cloth with soap, she noticed the stain colour changed to red, explain why?
Ans : Turmeric is a natural indicator which when reacts with bases turns it into red colour; here soap solution is basic so it turns red.

Q12: Explain why factory waste should be neutralised before disposing it into the water bodies.

Ans : The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances into it.

Long Q&A:

Q1:  State few properties of acids.

Ans : Acids are substances known for their sour taste (though tasting them is not safe). The word “acid” is derived from the Latin word ‘ACERE’, meaning sour. 

Properties of Acids: 

• Sour in taste. 
• Turn blue litmus paper red. 
• Turn China rose solution dark pink or magenta.

Examples of acidic substances include curd, vinegar, lemon, and orange juice, which all contain natural acids. 

Citrus Fruits are Acidic in Nature

Q2: State few properties of bases.

Ans : Bases are substances with a bitter taste and a slippery feel. 
Properties of Bases: 

• Bitter in taste. 
• Turn red litmus paper blue. 
• Turn turmeric paper reddish-brown. 
• Turn China rose solution green.

Some common examples of bases include baking soda, milk of magnesia, and soap. The chemical nature of these substances is referred to as basic. 

Q3: What are the differences between acids and bases?

Ans : 

Q4: Describe the process of neutralisation with the help of an example.

Ans : 

Neutralisation is a process in which an acid solution when mixed with base solution, react with each other to produce a salt and water along with generation of heat. Salt so produced, may be acidic, basic or neutral in nature. In this process the acidic nature of the acid and the basic nature of the base are destroyed.

NeutralizationAcid + base → salt + water. (heat is evolved)

For example: HCl + NaOH→ NaCl + H₂O.
Hydrochloric acid  + Sodiumhydroxide → Sodium chloride + Water 

Q5: Explain the process and treatment of an ant bite.

Ans: When an ant bites, it injects an acidic liquid called formic acid into the skin, causing burning pain, redness, and irritation. The effect of the acid can be neutralized by applying a mild base to the affected area.

Two common treatments are:

1. Baking soda solution: Baking soda (sodium hydrogen carbonate) neutralizes the acid and reduces the pain and irritation.
2. Calamine solution: Calamine contains zinc carbonate, which also neutralizes the acidic effect and provides relief.

Applying either of these substances helps neutralize the acid and reduce the discomfort caused by the ant bite.

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In This chapter there are no question. So we have added

🔍 Short Answer Questions

1. Q: What is science according to the introduction in Chapter 1?
   A: Science is described as a process of curiosity, asking questions, performing experiments, and exploring the world to understand natural phenomena.
2. Q: How does the textbook encourage students to learn science?
   A: By urging them to ask questions, do experiments, explore surroundings, and connect real-life experiences with science.
3. Q: What inspired early flight experiments as per the chapter?
   A: Observations of bird wings and simple paper planes inspired early inventors to study flight.
4. Q: What is meant by ‘the ever-evolving world of science’?
   A: It refers to the continuously growing and changing nature of scientific knowledge and discovery.
5. Q: How is the layout of the textbook described?
   A: The page numbers follow the playful path of a butterfly and a paper plane, symbolizing free exploration.

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🧠 Conceptual Questions

6. Q: Why does the textbook call science a way of thinking?
   A: Because science involves curiosity, questioning, reasoning, and openness to new information—not just memorizing facts.
7. Q: Give an example of how one area of science connects to another.
   A: Learning about light (physics) helps understand plant growth (biology) through photosynthesis.
8. Q: What does the chapter say about reversible and irreversible changes?
   A: Some changes like melting ice are reversible, while others like ripening fruits or burning wood are irreversible.
9. Q: What role does heat play in physical changes?
   A: Heat can cause substances to change state (like melting or evaporating) and can also speed up certain changes.
10. Q: How does the Sun contribute to the water cycle?
    A: The Sun heats water, causing evaporation, which leads to condensation and rainfall.

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✨ Creative & Exploratory Questions

11. Q: What question might lead to the answer “Because the cat’s teeth were crooked”?
    A: Why did the cat need braces?
12. Q: Suggest a question for the answer “Just add some milk.”
    A: How do I fix overly spicy cereal?
13. Q: Create a question that fits the answer “Don’t panic, I have my towel.”
    A: What did the space traveller say when the spaceship lost signal?
14. Q: What could be the question if the answer is “42”?
    A: What is the answer to life, the universe, and everything? (From The Hitchhiker’s Guide to the Galaxy)

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🧪 Activity-Based or Thinking Questions

15. Q: What kind of materials help a bulb glow in a simple circuit?
    A: Conductors like copper wires help the current pass and make the bulb glow.
16. Q: Why is it important to do experiments outside the textbook?
    A: Real-life experiments help connect theory with observation and develop scientific thinking.
17. Q: What is the link between human activity and environmental change as discussed?
    A: Human activities can disrupt natural balance, and science helps us understand and correct these effects.
18. Q: How does observing shadows help us understand time?
    A: Ancient humans used the changing position of shadows to estimate time, leading to sundials.

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✍️ Long Answer Questions

Q: Summarize how science is both discovery and responsibility as per the chapter.
A: Science helps us discover how nature works, but it also makes us aware of how human actions affect the environment. Being responsible means using scientific knowledge to build a more sustainable world.

Q: Explain how light helps us beyond just visibility, as explained in the chapter.
A: Light not only enables vision but also leads to scientific understanding of the universe. Its study helps explain shadows, time measurement, eclipses, and even the structure of the universe.