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Class 8 | Science | Textbook Solutions | Maharashtra Board

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 16 | Reflection Of Light | Exercise Solution | Maharashtra Board

1. Fill in the blanks: i. The perpendicular to the mirror at the point of incidence is called …………. .Answer:The perpendicular to the mirror at the point of incidence is called the normal. ii. The reflection of light from a wooden surface is ……….. reflection.Answer:The reflection of light from a wooden surface is irregular reflection. iii. The working of a kaleidoscope is based on the properties of …………… .Answer:The working of a kaleidoscope is based on the properties of reflection of light. 2. Draw a figure describing the following: The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, i draw the ray reflected from the second mirror. What will be its angle of reflection? Answer:For the ray C, the angle of reflection = 60°. 3. How will you explain the statement ‘We cannot see the objects in a dark room’? Answer:In a room that is completely dark, no light falls on objects. Hence, no light enters our eyes. Hence, there is no sensation of vision, i.e., we cannot see the objects. 4. Explain the difference between regular and irregular reflection of light. Answer:For regular reflection of light, the angles of incidence as well as the angles of reflection are the same for all parallel rays of light incident on the plane and smooth surface. Hence, the reflected rays are also parallel to one another. For irregular reflection of light, the angles of incidence for parallel rays of light incident on the rough surface are not equal, and hence the angles of reflection are also not equal. Here, the reflected rays are not parallel to one another and spread over a large surface. 5. Draw a figure showing the following:(a) Incident ray, (b) Normal, (c) Angle of incidence, (d) Angle of reflection, (e) Point of incidence, (f) Reflected ray. Answer: 6. Study the following incident. Swara and Yash were looking in a water-filled vessel. They could see their images clearly in the still water. At that instant, Yash threw a stone in the water. Now their images were blurred. Swara could not understand the reason for the blurring of the images.Explain the reason for blurring of the images to Swara by answering the following questions: I. Is there a relation between the reflection of light and the blurring of the images?Answer:Yes. ii. Which types of reflection of light can you notice from this?Answer:Regular reflection of light when light is incident on the still water and irregular reflection of light when light is incident on the water as ripples are produced on its surface when a stone is thrown in the water.Still water behaves as a plane and smooth surface while oscillating water behaves as a rough surface. iii. Are the laws of reflection followed in these types of reflection?Answer:Yes. 7. Solve the following examples. a. If the angle between the plane mirror and the incident ray is 40°, what are the angles of incidence and reflection?Solution:The angle between the plane mirror and the incident ray is 40°. Therefore, the angle of incidence (i) = the angle made by the incident ray with the normal to the plane mirror = 90° – 40° = 50°. The angle of reflection, r – i – 50°. b. If the angle between the mirror and reflected ray is 23°, what is the angle of incidence of the incident ray?Solution:The angle between the mirror and the reflected ray is 23°. Therefore, the angle of reflection (r) = the angle made by the reflected ray with the normal to the plane mirror = 90° – 23° = 67°.∴ The angle of incidence, i = r = 67°.

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 13 | Chemical Change and Chemical Bonds | Exercise Solution | Maharashtra Board

1. Complete the statement by filling the gaps using appropriate term from the terms given in the brackets:(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign) a. An ……….. is drawn in between the reactants and products while writing the equation for a chemical reaction.Answer:An arrow is drawn in between the reactants and products while writing the equation for a chemical reaction. b. Rusting of iron is a ……….. chemical change.Answer:Rusting of iron is a slow chemical change. c. The spoiling of food is a chemical change which is recognized from the generation of certain …………. due to it.Answer:The spoiling of food is a chemical change which is recognized from the generation of certain smell due to it. d. A colourless solution of calcium hydroxide in a test tube turns ………….. on blowing in it through a blow tube for some time.Answer:A colourless solution of calcium hydroxide in a test tube turns milky on blowing in it through a blow tube for some time. e. The white particles of baking soda disappear when put in lemon juice. This means that it is a ……….. change.Answer:The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change. f. Oxygen is a …………….. in respiration.Answer:Oxygen is a reactant in respiration. g. Sodium chloride is …………… compound while hydrogen chloride is compound.Answer:Sodium chloride is ionic compound while hydrogen chloride is covalent compound. h. Electron …………….. is complete in each hydrogen in a hydrogen molecule.Answer:Electron duplet is complete in each hydrogen in a hydrogen molecule. I. Chlorine (Cl2) molecule is formed by ………….. of electrons between two chlorine atoms.Answer:Chlorine (Cl2) molecule is formed by sharing of electrons between two chlorine atoms. 2. Explain by writing a word equation. a. Respiration is a chemical change.Answer:Respiration is a biological process, in this process air is inhaled, oxygen present in this inhaled air reacts with glucose present in the cells of the body forming carbon dioxide and water. Moreover, we cannot obtain glucose and oxygen from carbon dioxide and water. Hence, respiration is a chemical change.Word equation: b. Hard water gets softened on mixing with a solution of washing soda.Answer:Hard water does not form lather with soap and is brackish to taste. This is because hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state. When a solution of washing soda is added to hard water, it forms a precipitate of calcium carbonate and magnesium carbonate, which is removed by filtration thus water is softened.Word equation: c. Limestone powder disappears on adding to dilute hydrochloric acids.Answer:In the reaction of dil. HCl and limestone powder (CaCO3), limestone disappears slowly and carbon dioxide (CO2) liberates slowly.Word equation: d. Bubbles are seen on adding lemon juice to baking soda.Answer:When baking soda is added to lemon juice a chemical change takes place in citric acid present in the lemon juice and carbon dioxide gas is formed. Word equation: This is a neutralization reaction. 3. Match the pairs. Column I Column II 1. Photosynthesis a. Tendency to lose electrons 2. Water b. Reactant in combustion process 3. Sodium chloride c. Chemical change 4. Dissolution of salt in water d. Covalent bond 5. Carbon e. Ionic bond 6. Fluorine f. Physical change 7. Magnesium g. Tendency to form anion Answer: Column I Column II 1. Photosynthesis c. Chemical change 2. Water d. Covalent bond 3. Sodium chloride e. Ionic bond 4. Dissolution of salt in water f. Physical change 5. Carbon b. Reactant in combustion process 6. Fluorine g. Tendency to form anion 7. Magnesium a. Tendency to lose electrons 4. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms. a. Sodium Chloride: Answer:1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.2. Sodium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na+). 4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.5. Thus, the electron lost by sodium is taken up by chlorine. 6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP). 7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed. 8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule. b. Potassium fluoride:Answer:1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.2. Potassium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K+). 4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet. 5. Thus, the electron lost by potassium is taken up by chlorine. 6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F–). 7. Thus, a fluorine atom accepts one electron from

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 19 | Life Cycle Of Stars | Exercise Solution | Maharashtra Board

1. Search and you will find: a. Our galaxy is called ………… .Answer:Our galaxy is called the Milky Way and Mandakini. b. For measuring large distances, ………… is used as a unit.Answer:For measuring large distances, the light year is used as a unit. c. The speed of light is …………. km/s.Answer:The speed of light is 300000 km/s. d. There are about ………… stars in our galaxy.Answer:There are about 100 billion stars in our galaxy. e. The end stage of the Sun will be …………. .Answer:The end stage of the Sun will be a white dwarf. f. Stars are born out of ………… clouds.Answer:Stars are born out of interstellar clouds. g. Milky way is a ………. galaxy.Answer:Milky way is a spiral galaxy. h. Stars are gigantic spheres of ………… gas.Answer:Stars are gigantic spheres of hot gas. I. The masses of other stars are measured relative to the mass of the …………. .Answer:The masses of other stars are measured relative to the mass of the Sun. j. Light takes ……………. to reach us from the Sun while it takes …….. to reach us from the moon.Answer:Light takes about 8 minutes to reach us from the Sun while it takes about 1 second to reach us from the moon. k. The larger the mass of a star, the faster is its ……….. .Answer:The larger the mass of a star, the faster is its evolution. l. The number of fuels used in the life of a star depends on its …………. .Answer:The number of fuels used in the life of a star depends on its mass. 2. Who is telling lies? a. Light year is used to measure time.Answer:False. (Light year is used to measure distance.) b. End stage of a star depends on its initial mass.Answer:True. c. A star ends its life as a neutron star when the pressure of its electrons balances its gravity.Answer:False. (A star ends its life as a neutron star when the pressure of its neutrons balances its gravity.) d. Only light can emit from the black hole.Answer:False. (Not even light can be emitted by a black hole.) e. The Sun will pass through the supergiant stage during its evolution.Answer:False. (The Sun will pass through the red giant stage during its evolution.) f. The Sun will end its life as a white dwarf.Answer:True. 3. Answer the following question: a. How do stars form?Answer:There are huge clouds of gas and dust in the empty spaces between the stars in a galaxy. These clouds are called interstellar clouds. The size of an interstellar cloud is about a few light years. When an interstellar cloud starts contracting due to some disturbance, its density and temperature increase. This results in formation of a dense sphere of hot gas and nuclear energy generation starts at the centre of the star. Therefore, the gas sphere becomes self-luminous. Thus a star is formed, i.e., a star is born.A huge interstellar cloud can produce thousands of stars at a time. b. Why do stars evolve?Answer:Although stars appear stable for quite a long period of time, their properties do change, though very slowly. A change in the properties of a star, leading to its passing through different stages, is called evolution of the star. Burning of the fuel at the centre of the star and a gradual decrease in its amount is the main reason of evolution of a star. c. What are the three end stages of stars?Answer: d. Why was the name black hole given?Answer:When a star having initial mass larger than 25 times the mass of the Sun reaches its end stage, its gravitational force and density increase exponentially. All nearby objects get attracted towards the star and nothing can come out of it, not even light. All incident light is absorbed by the star. We can probably see a very minute black hole at its place. Hence, the name is given as black hole. e. Which types of stars end their life as a neutron star?Answer:Stars having initial mass between 8 and 25 times the mass of the Sun end up as neutron stars. When these stars pass through ( the supergiant stage, their size increases to 1000 times. Huge explosion that occurs in the last stage of these stars is very powerful and very high energy is given off. After the huge explosion, called the supernova explosion, their central portion contracts in size to about 10 km. In this stage, such stars are completely made up of neutrons and hence are called neutron stars. 4. A. If you are the Sun, write about your properties in your own words.B. Describe white dwarfs. Answer: If you are the Sun, write about your properties in your own words.Answer:There are billions of stars in the galaxy called the Milky Way and Mandakini. I am one of the small stars called the Sun. I have my own family called the solar system. There are planets, satellites, asteroids, comets and meteors in my family. My mass is 2 × 1030 kg which is about 3.3 lakh times that of the earth. With a radius of 695700 km, my size is about 100 times that of the earth. My surface temperature is about 5800 K while it is 1.5 × 107 K at the centre. 72 % of my mass consists of hydrogen while 26 % consists of helium. Rest 2 % is made up of elements heavier than helium. I am about 4.5 billion years old and the scientists on the earth have concluded that not much change has taken place in my properties during this period. According to the scientists, in the end stage of my life, I will turn into a red giant star. Thereafter, I will first explode and then contract to become as small as the earth. I will appear small as well as white and hence, I will be called a white dwarf. This will be my last stage for ever. Depending on the initial mass, stars can reach one of the three end stages. White dwarf is one such stage of stars having initial mass less than 8 times the mass of

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 15 | Sound | Exercise Solution | Maharashtra Board

1. Fill in the blank with appropriate word: a. The region in a sound wave, with higher pressure and density is called ………….. and that with low pressure and density is called ……….. .Answer:The region in a sound wave, with higher pressure and density is called compression and that with low pressure and density is called rarefaction. b. Medium is …………… for generation of sound.Answer:Medium is needed (or necessary) for generation of sound. c. The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is ………… .Answer:The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is 500 Hz.[Note: Total number: 100. ∴ 500 compressions and 500 rarefactions are produced per second.] d. Different sound notes have different ………………. .Answer:Different sound notes have different frequencies. e. In a loudspeaker, …………… energy is converted into ………….. energy.Answer:In a loudspeaker, mechanical energy is converted into sound energy. 2. Give scientific reasons: a. It is essential to change the tension in the vocal cords, as we produce different sound notes from our larynx.Answer:Different sound notes correspond to different frequencies. The frequency of sound depends on the tension in the vocal cords. Hence, it is essential to change the tension in the vocal cords, as we produce different sound notes our larynx. b. Astronauts on the moon cannot hear each other directly.Answer:Two astronauts on the moon talking to each other directly, will be unable to listen to each other, even if they are very close to each other. The moon does not have atmosphere. Since there is no medium which is necessary for generation and propagation of sound, between the astronauts, direct sound propagation between them is not possible. Therefore, the astronauts use some technology like the one used in our cell-phones to communicate with each other. The waves used in cell-phone do not need any medium for propagation. c. As the sound wave propagates from one place to the other in air, the air itself is not required to move from one place to the other.Answer:Propagation of sound through air occurs due to energy transfer by vibrating air molecules in one region to those in the adjacent region away from the source. The molecules simply vibrate about their mean positions. Hence, the air itself is not required to move from one place to the other. 3. How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation? Answer:1. Guitar: It is a string based, flat- backed instrument. It has usually six strings, the strings are plucked or strummed with the fingers or a small piece of plastic, wood, etc. It has a flat sounding board with a circular sound hole in the centre. Also it has a fretted fingerboard. Its frequency range is more than three octaves. The frequency of vibration of the string is changed by changing the tension in the string or changing the vibrating length of the string. As the tension is increased, the frequency increases. As the vibrating length is increased, the frequency decreases. This is how different sound notes are generated.[Note: The acoustic guitar has hollow body and six or twelve strings while the electric guitar usually has solid body and six strings. The electric bass guitar has four strings.] 2. Flute: It is a wind instrument where air is blown against the edge or rim of the blowing hole. The frequency of the sound produced depends upon the length of the vibrating air column in the tube. The greater the length of the vibrating air column, the less is the frequency of the sound produced. This is how different sound notes are produced. The flute has six or seven or eight holes to generate sounds of different frequencies. Different notes can be generated also by changing the way of air-blowing. 4. How is sound produced in the human larynx and a loudspeaker? Answer:1. Sound production in the human larynx:In the humans, sound is produced in the voice box called the larynx. It is located at the upper end of the windpipe. Two vocal cords (chords) are stretched across it with a narrow slit between them for the passage of air (Fig. 15.5). When the lungs force air through the slit, the cords start vibrating. The frequency of the sound produced depends upon the length and thickness of the cords, and the tension in the chords. The frequency increases with the increase in tension and the more the length or the thickness of the cord, the less is the frequency. Muscles attached to the cords can make the cords tight (more tension) or loose (less tension). 2. Sound produced in a loudspeaker:Figure shows the internal construction of a loudspeaker. Here, a coil is wound around a permanent magnet. The conical screen of the loudspeaker is attached to the coil. When a current is passed through the coil, a magnetic field is produced. Its interaction with the permanent magnet results in the back and forth motion of the coil. The frequency and the amplitude of the motion of the coil depends on the variation in the current through the coil. As the coil moves, the conical screen also moves back and forth. The vibrations of the screen produce sound waves in air. Very loud sound can be produced by changing the current.[Note: If you gently touch the vibrating screen, you can feel the vibrations.] 5. Explain the experiment, with a neat diagram, to prove the following:‘Sound needs a material medium for propagation.’ Answer: Figure shows part of the set up used in this experiment. What is not shown is the electric circuit in which the electric bell is connected. A vacuum tight bell jar contains an electric bell connected to a power supply through the lid of the jar. The jar is placed on a smooth horizontal surface such as that of glass. Initially the vacuum pump is off and

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 14 | Measurement and Effect Of Heat | Exercise Solution | Maharashtra Board

1. A. Whom should I pair with? Group ‘A’ Group ‘B’ 1. Temperature of a healthy human body a. 296 K 2. Boiling point of water b. 98.6 °F 3. Room temperature c. 0°C 4. Freezing point of water d. 212 °F Answer: Group ‘A’ Group ‘B’ 1. Temperature of a healthy human body b. 98.6 °F 2. Boiling point of water d. 212 °F 3. Room temperature a. 296 K 4. Freezing point of water c. 0°C 1.B. Who is telling the truth? a. The temperature of a substance is measured in joule.Answer:False. (The temperature of a substance is measured in °C or °F or K.) b. Heat flows from an object at higher temperature to an object at lower temperature.Answer:True. c. The joule is the unit of heat.Answer:True. d. Objects contract on heating.Answer:False. (In general, objects expand on heating. There are some exceptions to this, you will learn about them in Standard X.) e. Atoms of a solid are free.Answer:False. (Atoms of a solid are bound to each other due to the forces acting between them.) f. The average kinetic energy of atoms in a hot object is less than the average kinetic energy of atoms in a cold object.Answer:False. (The average kinetic energy of atoms in a hot object is more than the average kinetic energy of atoms in a cold object.) 1.C. You will find if you search. a. A thermometer is used to measure ……………. .Answer:A thermometer is used to measure temperature. b. The apparatus used to measure heat is called a ………… .Answer:The apparatus used to measure heat is called a calorimeter. c. Temperature is the measure of the …………. kinetic energy of the atoms in a substance.Answer:Temperature is the measure of the average kinetic energy of the atoms in a substance. d. The heat contained in a substance is the measure of the ………….. kinetic energy of the atoms in the substance.Answer:The heat contained in a substance is the measure of the total kinetic energy of the atoms in the substance. 2. Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why? Answer:Shivani’s tea will be ready first.Reason: In a given time, the amount of heat received by the vessel on a stove is far greater than that received by the vessel kept in a solar cooker. 3. Write brief answers. a. Describe a clinical thermometer. How does it differ from the thermometer used in a laboratory?Answer:A clinical thermometer has a narrow stem and a long bulb filled with mercury (or alcohol). There is a small constriction in the stem above the bulb. When the bulb of the thermometer is held in the armpit or the mouth of a patient, the mercury (or alcohol) in the bulb rises in the stem. When it is taken out of the patient’s body, the small constriction does not allow the mercury (or alcohol) from the stem to retreat into the bulb. Thus, this arrangement enables us to read the temperature of the patient’s body at ease after the removal of the thermometer from his body. The clinical thermometer is graduated from 35 °C to 42 °C (or from 95 °F to 108 °F). At 37 °C (98.6 °F), there is a red arrow mark which indicates the temperature of a healthy person. The thermometer used in a laboratory has wider range and does not have constriction like a clinical thermometer. b. What is the difference between heat and temperature?Answer:Heat is related to the total kinetic energy of the atoms in a substance while temperature is related to the average kinetic energy of the atoms in the substance. Heat flows from a body at higher temperature to a body at lower temperature. Thus, temperature is a quantity that determines the direction of flow of heat. It is a quantitative measure of the degree of hotness or coldness of a body. Higher temperature does not mean higher heat content. Suppose a vessel A contains 2 litres of water at 90 °C and a vessel B contains 100 ml of water at 91 °C. Then the heat content of water in A is greater than that of water in B, but the temperature of water in B is higher than that of water in A. Units of heat:Heat is usually expressed in calorie, kilocalorie and joule. It can also be expressed in erg as heat is a form of energy. c. Explain the construction of a calorimeter. Draw the necessary figure.Answer: Figure shows the construction of a calorimeter. Like a thermo flask, a calorimeter has two vessels. The inner vessel, made of copper, is (practically) thermally isolated from the surroundings. The outer vessel is made of wood and is covered with a heat resistant lid. The lid has two holes, one for the thermometer and the other for the stirrer. The inner and outer surfaces of the inner vessel are polished for minimizing exchange of heat with the surroundings by radiation. A heat resistant ring covers the inner vessel. d. Explain why rails have gaps at specific distances.Answer:The rails expand in summer due to increase in the temperature of the atmosphere. Also, they expand due to rise in temperature caused by the friction between the rails and the wheels of the running train. If there is no gap between successive rails of a railway line, the rails would bend due to expansion. This bending and twisting of the rails would cause accidents. Hence, a gap is kept between successive rails of a railway line to make provision for their expansion in summer. Do you know: Have you seen rails? They are not continuous. A small gap is kept between them at regular intervals. This is shown in the figure. This is kept to accommodate the change in the length of the rails with change in temperature. If this gap is not kept, then the rail will get distorted due to expansion in summer

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 12 | Introduction To Acid and Base | Exercise Solution | Maharashtra Board

1. Identify the following solutions, whether they are acid or base. 2. Write chemical names from given formulae.H2SO4, Ca(OH)2, HCl, NaOH, KOH, NH4OH Answer: 3. Sulphuric acid has highest importance in chemical Industry. Why? Answer:Sulphuric acid has highest importance in the chemical industry because it is used in the manufacturing of fertilizers like ammonium sulphate and superphosphate of lime. It is used in the manufacturing of hydrochloric acid, nitric acid, phosphoric acid, ether, plastics and metal sulphates. It is also used in the manufacturing of dyes, drugs, perfumes, disinfectants and glue. 4. Give answers. a. Which acid is used for getting chloride salt?Answer:Hydrochloric acid is used for getting chloride salt. b. By squeezzing lemon on a piece of rock the gas liberated turned lime water milky. Which compound is present in the rock?Answer:Metal carbonate is present in the rock. c. The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not?Answer:The chemical is tested with blue litmus paper. If it turns red it is an acidic otherwise tested with red litmus paper, if it turns blue, it is an alkaline. 5. Answer the following questions. a. Explain the difference between acid and base.Answer:Acids: Bases: b. Why indicator does not affect by salt?Answer:Mostly indicators are organic compounds which do not react with a salt. c. Which substances are produced i by neutralization process?Answer:Salt and water are produced in the f neutralization process. d. Which are the industrial uses of acids?Answer:Acids which are used in the industry are: 1. Sulphuric acid: Sulphuric acid is 5 used (a) in the manufacture of chemical? fertilizers like ammonium sulphate, (b) for cleaning gold and silver articles and (c) in car batteries. 2. Hydrochloric acid: Hydrochloric acid is used (a) to clean toilets and (b) to obtain glucose from starch and also for producing gelatine. 3. Nitric acid: Nitric acid is used (a) in the manufacture of perfumes (b) for engraving on copper, brass or silver and (c) in the manufacture of paints and explosives. 6. Select proper word given in bracket and fill in the blanks. a. Main constituent of acid is ……………. .Answer:Main constituent of acid is H+ ion. b. Main constituent of alkali is …………….. .Answer:Main constituent of alkali is OH– ion. c. Tartaric acid is a …………… acid.Answer:Tartaric acid is a weak acid. 7. Match the pairs. Group A Group B 1. Tamarind a. Acetic acid 2. Curd b. Citric acid 3. Lemon c. Tartaric acid 4. Vinegar d. Lactic acid Answer: Group A Group B 1. Tamarind c. Tartaric acid 2. Curd d. Lactic acid 3. Lemon b. Citric acid 4. Vinegar a. Acetic acid 8. State true or false. a. Oxides of metals are alkaline in nature.Answer:True. b. Salt is acidic.Answer:False. (Salt is neutral) c. Metal corrodes due to salts.Answer:False. (Acids and bases corrode metals) d. Salts are neutral.Answer:True. (Not all salts neutral) 9. Classify the following substances into acidic, basic and neutral group:HCl, NaCl, MgO, KCl, CaO, H2SO4, HNO3, H2O and Na2CO3. Answer: Group Substances Acid HCl, H2SO4, HNO3 Base CaO, MgO, Na2CO3 Neutral H2O, NaCl, KCl.

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 18 | Ecosystem | Exercise Solution | Maharashtra Board

1. Complete the following by using the correct option: a. Air, water, minerals, soil are ………….. factors of an ecosystem. (physical, organic, inorganic)Answer:Air, water, minerals, soil are physical factors of an ecosystem. b. River, ponds, ocean are …………. ecosystems, (land, aquatic, synthetic)Answer:River, ponds, ocean are aquatic ecosystems. c. Man is ………….. in an ecosystem. (producer, consumer, decomposer)Answer:Man is consumer in an ecosystem. 2. Match the following: Producer Ecosystem 1. Cactus a. Forest 2. Aquatic plants b. Creek 3. Mangroves c. Aquatic 4. Pine d. Desert Answer: Producer Ecosystem 1. Cactus d. Desert 2. Aquatic plants c. Aquatic 3. Mangroves b. Creek 4. Pine a. Forest 3. Give my information: a. Ecosystem.Answer:Ecosystem is the structure formed by the interrelationships between the living organisms and non-living components in their surrounding habitats. Living organisms are also called biotic factors while the non-living components are called abiotic factors. The abiotic and biotic factors have a reciprocal relationship with each other. The ecosystem has plants as producers, animals as consumers and microbes as decomposers. The decomposers return the substances back to the nature by process of decomposition in which the organic complex molecules are reduced to their inorganic constituents. Thus the dead remains of plants and animals are once again recycled back to the nature in any healthy ecosystem. b. Biome.Answer:Biomes are a larger collection of small ecosystems which are similar in their structure. In a particular biome there are same climatic, abiotic factors and similar living organisms. Biomes are of two main types, land biomes and aquatic biomes. The land biomes exist only on land. Land biomes are of following subtypes based on the abiotic factors. E.g. Grasslands, evergreen forests, deserts, Tundra ecosystem, ecosystems in Taiga, tropical rainforests, etc. Aquatic biomes include freshwater ecosystem, marine ecosystem and brackish water ecosystem found in the creeks. c. Food web.Answer:The complex feeding relationships form a food web. In nature in any ecosystem, the food chains are not straight and linear. But these are quite complex. A prey is consumed by a predator but this predator can itself be a prey to some other predator. E.g. Frog is a predator for variety of insects but frog is preyed upon by snake and the snake can be eaten by a bird. The same bird can also feed on insects or frog. The interrelationships between different biotic components of any ecosystem thus form the complicated food web. 4. Give scientific reasons: a. Plants in an ecosystem are called producers.Answer:are cut down causing deforestation. The wild animals lose their habitat. Many of them become extinct. There is great loss of flora and fauna due to construction of large dams. There is undue pressure on the land surface caused due to stored water column. This may cause earthquakes. The human settlements are removed as their houses and farms are immersed under water. In all the above ways large dams destroy the ecosystems. b. Large dams destroy ecosystems.Answer:When a large dam is constructed, the original landscape is changed. The trees are cut down causing deforestation. The wild animals lose their habitat. Many of them become extinct. There is great loss of flora and fauna due to construction of large dams. There is undue pressure on the land surface caused due to stored water column. This may cause earthquakes. The human settlements are removed as their houses and farms are immersed under water. In all the above ways large dams destroy the ecosystems. c. Rhinos were restored in Dudhwa forest.Answer:Long ago in last century, Dudhwa forest was the natural habitat of the one-horned Rhino. However, due to hunting and poaching, the Rhino became almost extinct. In order to restore it back the breeding in captivity was attempted and the young ones were released in the natural habitat. Saving the precious wildlife is important and hence these efforts were done. 5. Answer the following: a. What are the effects of increased population (of human beings) on ecosystems?Answer: b. How is urbanization responsible for destruction of ecosystems?Answer:When people do not get sufficient food and other amenities, they migrate to the cities. The cities provide employment for many people due to industries, factories and other facilities. Every day many people migrate to cities. This causes urbanization. Due to increased population in cities, there is more need for housing. This results in loss of agricultural lands, marshlands, wetlands, forests and grasslands, etc. The natural ecosystems are lost in an attempt to have developmental work. Human interference causes changes in the ecosystems. When land usage is changed many naturally occurring species of plants and animals are exterminated. Animal- human conflicts are very common in newly established urban areas which are near the natural forests. c. What are the reasons for war?Answer:There are difference of opinions and competition over land, water, mineral resources, etc. among neighbouring countries. Moreover, there can be economic and political causes which lead to war among different countries. Many times the l religions and ethnicity are also caused for dispute. Due to international conflicts, the peace is disturbed and it results in war. d. Explain the interactions among the factors of an ecosystem.Answer: e. Differentiate between evergreen forests and grasslands.Answer: Evergreen forests Grasslands 1. About seven percent of the Earth’s surface is occupied by evergreen forests. 1. About 30 percent of the Earth’s surface is covered by grasslands. 2. More than half of the earth’s terrestrial plants and animals are seen in evergreen forests. 2. Grazing animals are seen in grasslands. 3. Tropical evergreen forests are dense, multi-layered. 3. Grasslands consist of tall grass. There are wild grasses and there may be some trees. 4. These forests are found in the areas receiving more than 200 cm annual rainfall i.e. very heavy rainfall. 4. There is an average of 20 – 35 inches of rainfall a year in grasslands. 5. Tropical regions show evergreen forests. 5. Several parts of the world have grasslands. 6. Describe the following pictures: Answer:The picture no. 1 is showing desert ecosystem, while the picture no. 2 is showing a forest ecosystem where a wetland (a lake)

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Class 8 | Science | Chapter 11 | Human Body and Organ System | Exercise Solution | Maharashtra Board

Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 11 | Human Body and Organ System | Exercise Solution | Maharashtra Board

1. Find out my partner. Group ‘A’ Group ‘B’ 1. Heartbeats a. 350 ml 2. RBC b. 7.4 3. WBC c. 37° C 4. Blood donation d. 72 per min 5. Normal body temperature e. 50 – 60 lakh/mm3 6. pH of oxygenated blood f. 5000 – 6000 per mm3 Answer: Group ‘A’ Group ‘B’ 1. Heartbeats d. 72 per min 2. RBC e. 50 – 60 lakh/mm3 3. WBC f. 5000 – 6000 per mm3 4. Blood donation a. 350 ml 5. Normal body temperature c. 37° C 6. pH of oxygenated blood b. 7.4 2. Complete the following table. Question a. Answer: 3. Draw neat and labeled diagrams. a. Respiratory system.Answer: b. Internal structure of heart.Answer: 4. Explain with reasons. a. Human blood is red coloured.Answer:The red colour of human blood is due to hemoglobin which is a red coloured conjugated protein with iron that is present on the red blood cells. Therefore, it looks red. b. Upward and downward movement of diaphragm occurs consecutively.Answer:The breathing movements are possible due to contraction and relaxation of the diaphragm. The rib muscles also help in these movements. When the ribs rise and diaphragm is lowered at the same time, then there is a decrease in pressure on lungs. This causes movement of air into the lungs at the time of inhalation. On the other hand, when ribs come back to their normal position and diaphragm is risen, then pressure on the lungs increases. This causes movement of the air out of the body through the nose in the form of exhalation. These movements are possible only due to consecutive upward and downward movement of the diaphragm. c. Blood donation is considered to be superior of all donations.Answer:Blood cannot be manufactured by any artificial chemical process. The only way to obtain blood is by donations of blood from a live donor. Blood is needed at times of emergency. The life of person can be saved if timely blood transfusion is given to the needy victim or a patient. Since such donation can save a valuable human life, it is called superior of all donations. d. Person with ‘O’ blood group is considered as ‘universal donor’.Answer:Person with ‘O’ blood group does not have any antigen on his/her RBCs. The ‘O’ type blood thus cannot cause clotting reactions in the body of the recipients. Such persons with ‘O’ blood group can donate blood to any person having any blood group therefore they are considered as ‘universal donor’. e. Food must have limited amount of salts.Answer:More salt in diet means more sodium ions. These extra sodium salts cause rise in blood pressure. Such condition is called hypertension. This condition can be dangerous and fatal in some cases. Therefore, one must keep control over sodium content of the food. 5. Answer the following questions in your own words. a. Explain the functional correlation of circulatory system with respiratory, digestive and excretory system.Answer:1. Three systems viz. respiratory, digestive and circulatory always work in coordination.2. Digestive system helps in breaking down complex food molecules into simple soluble nutrients at the end of the digestion process.3. The soluble nutrients are absorbed in the circulating blood in the villi of the intestine.4. The blood carries these nutrients to each cell during its circulation.5. The respiratory system helps the oxygen from the air to be absorbed in the blood.6. This process takes place in alveolus present in lungs. The oxygen is absorbed in the blood and through haemoglobin it is taken to every cell of the body. At the same time the unwanted carbon dioxide produced in each cell is given out in a process of gaseous exchange.7. The soluble nutrients, and chiefly glucose is metabolized with the help of oxygen-producing energy. Thus, all the three systems bring about coordinated functions to keep the body alive. b. Explain the structure and function of human blood.Answer:I. Structure, i.e. components of the human blood: Human blood is a fluid connective tissue consisting of blood plasma and blood corpuscles suspended in it. 1. Plasma: Plasma is the fluid part of the blood which is pale yellow in colour. It is slightly alkaline in nature. It has 90-92% water, 6-8 % proteins and 1-2 % inorganic salts.It contains proteins such as albumin, globulin, fibrinogen, etc. There are inorganic ions such as Ca, Na and K. 2. Blood cells:a. Blood cells are mainly of three types, viz. RBCs, WBCs and blood platelets. They are produced in the red bone marrow.b. RBCs are small, circular and enucleated cells. They are full of haemoglobin which is essential in transporting oxygen. RBCs are red blood cells which are 50 to 60 lakh per cubic millimetre. Their life span is 100 to 127 days.c. WBCs are large, nucleated and colourless. They are of five subtypes, viz. neutrophils, basophils, eosinophils, monocytes and lymphocytes. They are 5 to 10 thousands per millimetre of blood.d. Platelets are very small disc-shaped blood cells which are 2.5 to 4 lakh per cubic millimetre of blood. II. Function of human blood: 1. Transport functions: 2. Protection: Antibodies are produced in the blood and they protect the body from microbes and other harmful particles.3. Thermoregulation: Body temperature is maintained constant at 37 °C by vasodilation and vasoconstriction.4. Maintaining the balance of minerals like Na, K in the body.5. If bleeding occurs at the injury, platelets and a protein called fibrinogen of the blood form a clot and seal the injury.6. Functions of blood cells: c. Explain the importance and need of blood donation.Answer:Blood can never be synthesized artificially. There is no substitute for natural blood. Every healthy person possesses about 5 litres of blood in his or her body. In case of haemorrhage i.e. blood loss, the blood volume may reduce which can result into threat to life. Moreover, the loss of blood should be immediately taken care of, otherwise it may cost the life. Therefore blood transfusion is very crucial in case of victims of accidents, patients of surgeries or mothers who suffer from

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 17 | Man Made Material | Exercise Solution | Maharashtra Board

1. Try to find it: a. Plastic shows …………. property, hence it can be moulded to any shape.Answer:Plastic shows plasticity property, hence it can be moulded to any shape. b. Motor cars are coated with ……… .Answer:Motor cars are coated with Teflon. c. Thermocol melts at ………… °C.Answer:Thermocol melts at more than 100 °C (it is about 240 °C). d. …………….. glass dissolves in water.Answer:Alkali silicate or water glass dissolves in water. 2. Who is my partner? Column ‘A’ Column ‘B’ 1. Lead glass a. Plates 2. Bakelite b. Mattresses 3. Thermocol c. Electric bulb 4. Optic glass d. Electric switch 5. Polypropylene e. Lens Answer: Column ‘A’ Column ‘B’ 1. Lead glass c. Electric bulb 2. Bakelite d. Electric switch 3. Thermocol a. Plates 4. Optic glass e. Lens 5. Polypropylene b. Mattresses 3. Answer the following. a. Thermocol is produced from which material?Answer:Thermocol is made from polystyrene which is also a complex thermoplastic substance. b. Write uses of PVC.Answer:PVC or Polyvinyl chloride is used for making bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys, etc. c. Write the natural or man-made raw material of the following items.Mattress, beaker, bangle, chair, gunny bag, broom, knife, pen.Answer: Items Natural raw material Man-made raw materials Mattress Cotton, Coir (Jute fibres) Polypropylene Beaker ___ Glass (Silicate or borosilicate glass) Bangle Gold, silver, lac, copper Plastic, Glass Chair Wood Plastic (PVC) Gunny bag Jute, cotton Plastic (PVC) Broom Plant fibres Plastic fibres (PVC) Knife Metals such as iron Plastic Pen Metals Plastic d. Which are the main ingredients of glass?Answer:The main ingredients of glass are sand and silica. e. How the plastic is produced?Answer: 4. Distinguish between. a. Man-made material and natural materialAnswer: Man-made material Natural material 1. The man-made materials are obtained from processes in scientific laboratory. 1. Natural materials are obtained from nature. 2. Man-made materials are subjected to rigorous processing to alter the material for serving the intended purpose. 2. Natural materials are subjected to less treatment and processing. 3. Man-made materials are typically much more durable having a very long lifespan. 3. Natural materials have shorter lifespan, because these materials were once alive and so gradually perish over time. 4. Maintaining man-made materials require less care and attention. 4. Maintaining natural materials requires lots of care and continuous attention. 5. Man-made materials can have a negative environmental impact because they are not sustainable.E.g. Glass, plastic, Thermocol, soil, metals, rubber. 5. Natural materials do not have a negative environmental impact because they can be degraded easily.E.g. Cotton, silk, wood. b. Thermoplastic and Thermosetting plastic:Answer: Thermoplastic Thermosetting plastic 1. The plastic that can be moulded as per our wish is called thermoplastic. 1. The plastic in which a specific shape is given with the help of mould and this shape cannot be changed again on heating is called thermosetting plastic. 2. Thermoplastic substances can be recycled and reused.E.g. PVC – Polyvinyl chloride, PS – Polystyrene, PE – Polyethylene and PP – Polypropylene are types of thermoplastics. 2. Thermosetting plastic cannot be reused again.E.g. Bakelite, Melamine, Polyurethane and polyster are the types of thermosetting plastics. 5. Answer the following in your own words. a. Explain the effect of following materials on environment and human health.1. Plastic2. Glass.3. Thermocol.Answer:1. Plastic: 2. Glass: 3. Thermocol: b. Which measures will you arrange to minimize the environmental problems arising due to non-degradable plastic?Answer: 6. Write short notes. a. Glass production:Answer:The general preparation of the glass is as follows: b. Optic glass:Answer: c. Uses of plastic:Answer:Plastic, the man-made material is used in various forms in modern age. According to the type of plastic, its uses are different. I. Thermoplastic materials are used for manufacturing following articles: II. Thermosetting plastic is used in the manufacturing of the following items:

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