Brain Grain · braingrain.in
Science — Practice Paper · Set 1
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.Butanone is a four-carbon compound with the functional groupa. carboxylic acid.b. aldehyde.c. ketone.d. alcohol.[1]
2.Which of the following pairs will give displacement reactions?a. NaCl solution and copper metalb. MgCl₂ solution and aluminium metalc. FeSO₄ solution and silver metald. AgNO₃ solution and copper metal.[1]
3.The autotrophic mode of nutrition requiresa. carbon dioxide and water.b. chlorophyll.c. sunlight.d. all of the above.[1]
4.Which of the following methods is suitable for preventing an iron frying pan from rusting?a. Applying greaseb. Applying paintc. Applying a coating of zincd. All of the above.[1]
5.Which of the following constitute a food-chain?a. Grass, wheat and mangob. Grass, goat and humanc. Goat, cow and elephantd. Grass, fish and goat[1]
6.Which one of the following materials cannot be used to make a lens?a. Waterb. Glassc. Plasticd. Clay[1]
7.10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will bea. 4 mLb. 8 mLc. 12 mLd. 16 mL[1]
8.Where should an object be placed in front of a convex lens to get a real image of the size of the object?a. At the principal focus of the lensb. At twice the focal lengthc. At infinityd. Between the optical centre of the lens and its principal focus.[1]
9.The kidneys in human beings are a part of the system fora. nutrition.b. respiration.c. excretion.d. transportation.[1]
10.Fe₂O₃ + 2Al → Al₂O₃ + 2Fe. The above reaction is an example of aa. combination reaction.b. double displacement reaction.c. decomposition reaction.d. displacement reaction.[1]
11.Which of the following lenses would you prefer to use while reading small letters found in a dictionary?a. A convex lens of focal length 50 cm.b. A concave lens of focal length 50 cm.c. A convex lens of focal length 5 cm.d. A concave lens of focal length 5 cm.[1]
12.While cooking, if the bottom of the vessel is getting blackened on the outside, it means thata. the food is not cooked completely.b. the fuel is not burning completely.c. the fuel is wet.d. the fuel is burning completely.[1]
13.The brain is responsible fora. thinking.b. regulating the heart beat.c. balancing the body.d. all of the above.[1]
14.Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.i. (a) and (b)ii. (a) and (c)iii. (a), (b) and (c)iv. all[1]
15.A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is –a. 1/25b. 1/5c. 5d. 25[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.[2]
17.The radius of curvature of a spherical mirror is 20 cm. What is its focal length?[2]
18.Why is sodium kept immersed in kerosene oil?[2]
19.What are the differences between autotrophic nutrition and heterotrophic nutrition?[2]
20.A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?[2]
21.An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focussed image can be obtained? Find the size and the nature of the image.[2]
22.What happens at the synapse between two neurons?[2]
23.On what factors does the resistance of a conductor depend?[2]
24.How is the sex of the child determined in human beings?[2]
25.What is the role of the acid in our stomach?[2]
26.Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.[2]
27.What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?[2]
28.What is the importance of DNA copying in reproduction?[2]
29.What is meant by saying that the potential difference between two points is 1 V?[2]
30.If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?[2]
31.What is the common name of the compound Ca(ClO)₂?[2]
32.How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide?[2]
33.Judge the equivalent resistance when the following are connected in parallel – (a) 1 Ω and 10⁶ Ω, (b) 1 Ω and 10³ Ω, and 10⁶ Ω.[2]
🔑 Show Answer Key — Set 1
- 1. (c) ketone.
- 2. (d) AgNO₃ solution and copper metal.
- 3. (d) all of the above.
- 4. (c) Applying a coating of zinc
- 5. (b) Grass, goat and human
- 6. (d) Clay
- 7. (d) 16 mL
- 8. (b) At twice the focal length
- 9. (c) excretion.
- 10. (d) displacement reaction.
- 11. (c) A convex lens of focal length 5 cm.
- 12. (b) the fuel is not burning completely.
- 13. (d) all of the above.
- 14. (i) (a) and (b)
- 15. (d) 25
- 16. The image is formed about 8.6 cm behind the mirror. It is virtual, erect and diminished, with size about 2.1 cm.
- 17. The focal length is 10 cm.
- 18. Sodium is very reactive and reacts vigorously with oxygen and moisture in air, producing heat and possibly catching fire. It is kept under kerosene oil to prevent contact with air and water.
- 19. In autotrophic nutrition, organisms make their own food from CO₂ and water using light energy and chlorophyll, as green plants do. In heterotrophic nutrition, organisms depend on other organisms for ready-made organic food, as animals, fungi and many bacteria do.
- 20. A concave, or diverging, lens should be used. It diverges light from distant objects so that the image is formed on the retina of the myopic eye.
- 21. The screen should be placed 54 cm in front of the mirror. The image size is 14 cm, and the image is real, inverted and enlarged.
- 22. At a synapse, the electrical impulse at the end of one neuron causes release of chemical neurotransmitters. These chemicals cross the synaptic gap and start a new electrical impulse in the next neuron.
- 23. Resistance depends on the length of the conductor, its area of cross-section, the nature of its material and its temperature. It increases with length and decreases with cross-sectional area.
- 24. Human females have XX sex chromosomes and males have XY. The mother always contributes an X chromosome. The father contributes either X or Y. If the sperm carrying X fertilises the egg, the child is XX female; if the sperm carrying Y fertilises it, the child is XY male.
- 25. Hydrochloric acid in the stomach creates an acidic medium needed for the enzyme pepsin to digest proteins. It also helps kill many microbes that enter with food.
- 26. Heat (thermal decomposition): CaCO₃(s) → CaO(s) + CO₂(g) Light (photolytic decomposition): 2AgCl(s) → 2Ag(s) + Cl₂(g) Electricity (electrolytic decomposition): 2H₂O(l) → 2H₂(g) + O₂(g)
- 27. In parallel, each device gets the full potential difference of the source and can be switched on or off independently. If one device fails, the others continue to work. Parallel connection also allows each device to draw current according to its own resistance.
- 28. DNA copying passes genetic information from parents to offspring. It also produces small variations during copying, and these variations help populations adapt and survive in changing environments.
- 29. The potential difference between two points is 1 V if 1 joule of work is done to move 1 coulomb of charge from one point to the other: 1 V = 1 J C⁻¹.
- 30. No. Copper-T prevents pregnancy mainly by preventing implantation or fertilisation, but it does not prevent contact with infected body fluids. Barrier methods such as condoms help protect against sexually transmitted diseases.
- 31. The common name of Ca(ClO)₂ is bleaching powder.
- 32. Adding excess base increases the concentration of OH⁻ ions in the solution. The solution becomes more basic and its pH increases.
- 33. In both cases the equivalent resistance is slightly less than 1 Ω; practically, it is about 1 Ω.
Brain Grain · braingrain.in
Science — Practice Paper · Set 2
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field isa. towards southb. towards eastc. downwardd. upward[1]
2.The breakdown of pyruvate to give carbon dioxide, water and energy takes place ina. cytoplasm.b. mitochondria.c. chloroplast.d. nucleus.[1]
3.The human eye forms the image of an object at itsa. cornea.b. iris.c. pupil.d. retina.[1]
4.The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due toa. presbyopia.b. accommodation.c. near-sightedness.d. far-sightedness.[1]
5.Ethane, with the molecular formula C₂H₆ hasa. 6 covalent bonds.b. 7 covalent bonds.c. 8 covalent bonds.d. 9 covalent bonds.[1]
6.Which of the following correctly describes the magnetic field near a long straight wire?a. The field consists of straight lines perpendicular to the wire.b. The field consists of straight lines parallel to the wire.c. The field consists of radial lines originating from the wire.d. The field consists of concentric circles centred on the wire.[1]
7.Which of the following are environment-friendly practices?a. Carrying cloth-bags to put purchases in while shoppingb. Switching off unnecessary lights and fansc. Walking to school instead of getting your mother to drop you on her scooterd. All of the above[1]
8.Asexual reproduction takes place through budding ina. Amoeba.b. Yeast.c. Plasmodium.d. Leishmania.[1]
9.Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –a. 1:2b. 2:1c. 1:4d. 4:1[1]
10.The least distance of distinct vision for a young adult with normal vision is abouta. 25 m.b. 2.5 cm.c. 25 cm.d. 2.5 m.[1]
11.Which of the following is a plant hormone?a. Insulinb. Thyroxinc. Oestrogend. Cytokinin.[1]
12.An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –a. 100 Wb. 75 Wc. 50 Wd. 25 W[1]
13.A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted asa. TTWWb. TTwwc. TtWWd. TtWw[1]
14.Food cans are coated with tin and not with zinc becausea. zinc is costlier than tin.b. zinc has a higher melting point than tin.c. zinc is more reactive than tin.d. zinc is less reactive than tin.[1]
15.Which one of the following types of medicines is used for treating indigestion?a. Antibioticb. Analgesicc. Antacidd. Antiseptic[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.Differentiate between metal and non-metal on the basis of their chemical properties.[2]
17.Draw the structure of a neuron and explain its function.[2]
18.How do we detect the smell of an agarbatti (incense stick)?[2]
19.Why is a normal eye not able to see clearly the objects placed closer than 25 cm?[2]
20.What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)[2]
21.Why is the use of iodised salt advisable?[2]
22.How are involuntary actions and reflex actions different from each other?[2]
23.What is the role of the seminal vesicles and the prostate gland?[2]
24.Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?[2]
25.State two ways to prevent the rusting of iron.[2]
26.Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.[2]
27.How does our body respond when adrenaline is secreted into the blood?[2]
28.Give any two ways in which biodegradable substances would affect the environment.[2]
29.What do you mean by a precipitation reaction? Explain by giving examples.[2]
30.What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?[2]
31.Outline a project which aims to find the dominant coat colour in dogs.[2]
32.What are alloys?[2]
33.What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?[2]
🔑 Show Answer Key — Set 2
- 1. (d) upward
- 2. (b) mitochondria.
- 3. (d) retina.
- 4. (b) accommodation.
- 5. (b) 7 covalent bonds.
- 6. (d) The field consists of concentric circles centred on the wire.
- 7. (d) All of the above
- 8. (b) Yeast.
- 9. (c) 1:4
- 10. (c) 25 cm.
- 11. (d) Cytokinin.
- 12. (d) 25 W
- 13. (c) TtWW
- 14. (c) zinc is more reactive than tin.
- 15. (c) Antacid
- 16. Metals usually lose electrons to form positive ions, while non-metals gain or share electrons to form negative ions or covalent compounds. Metals form basic or amphoteric oxides; non-metals generally form acidic oxides. Metals react with dilute acids to produce hydrogen gas if they are above hydrogen in the reactivity series; non-metals generally do not. Metals form ionic chlorides such as NaCl, while non-metals often form covalent chlorides such as CCl₄.
- 17. A neuron has dendrites, a cell body with nucleus, a long axon and axon terminals. Dendrites receive information from receptors or other neurons. The impulse passes through the cell body and along the axon. At the axon terminal, chemicals are released across the synapse to pass the signal to another neuron, muscle or gland.
- 18. The smell molecules from the agarbatti reach olfactory receptors in the nose. These receptors generate nerve impulses that travel to the brain, where the smell is interpreted.
- 19. For objects closer than 25 cm, the ciliary muscles cannot make the eye lens sufficiently thick to reduce its focal length enough. The image is not focused sharply on the retina, so the object appears blurred.
- 20. A sulphur molecule is S₈. The eight sulphur atoms are joined in a ring by single covalent bonds; each sulphur shares one electron with each of two neighbouring sulphur atoms and has two lone pairs remaining.
- 21. Iodised salt supplies iodine, which is needed by the thyroid gland to make thyroxine. Thyroxine regulates metabolism, and iodine deficiency can cause goitre and related disorders.
- 22. Involuntary actions are automatic actions not under conscious control, such as heartbeat and breathing, and are often controlled by the brain. Reflex actions are sudden automatic responses to a specific stimulus, such as pulling a hand away from a hot object, usually mediated through the spinal cord.
- 23. The seminal vesicles and prostate gland add fluids to sperm to form semen. These secretions provide nutrition, make transport easier and create a medium in which sperm can move.
- 24. Complex organisms have specialised tissues, organs and organ systems. Regeneration can repair or replace some parts, but a small piece usually cannot reorganise itself into all the specialised structures needed for a complete organism.
- 25. Rusting of iron can be prevented by painting/oiling/greasing the surface to keep air and moisture away, and by galvanising it with a coating of zinc.
- 26. Using the right-hand rule, if the current appears clockwise when viewed from above the table, the magnetic field inside the loop is directed downward, into the table. Outside the loop, the field lines return upward, out of the table.
- 27. Adrenaline prepares the body for emergency action. The heart beats faster, breathing rate increases, blood flow to muscles increases, blood flow to the digestive system and skin decreases, and stored glucose is made available for energy.
- 28. Biodegradable substances can release foul smell and provide breeding places for disease-causing organisms if they accumulate. During decomposition they may also release gases and organic matter that can pollute air or water if not managed properly.
- 29. A precipitation reaction is a reaction in which two solutions react to form an insoluble solid called a precipitate. For example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq), in which insoluble white barium sulphate is formed as a precipitate. Another example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq), where white silver chloride is precipitated.
- 30. Movement in a sensitive plant is caused by changes in water pressure in specialised cells and does not involve nerves or muscles. Movement in our legs is caused by contraction and relaxation of muscles under nervous control.
- 31. Collect data on coat colour of many parent dogs and their puppies over several generations. Record crosses between pure-breeding parents of different colours if possible. If all F₁ offspring show one colour and the other colour reappears in later generations, the F₁ colour is likely dominant. A large sample is needed because dog coat colour can involve more than one gene.
- 32. Alloys are homogeneous mixtures of two or more metals, or of a metal and a non-metal. Examples include brass, bronze and steel.
- 33. Receptors detect stimuli such as light, sound, smell, taste, touch, heat or pain and send signals to the nervous system. If receptors do not work properly, the body may fail to detect danger or changes in the environment, such as not smelling smoke, not feeling burns, or having poor vision or hearing.
Brain Grain · braingrain.in
Science — Practice Paper · Set 3
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution containsa. NaClb. HClc. LiCld. KCl[1]
2.The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?a. Between the principal focus and the centre of curvatureb. At the centre of curvaturec. Beyond the centre of curvatured. Between the pole of the mirror and its principal focus.[1]
3.At the time of short circuit, the current in the circuita. reduces substantially.b. does not change.c. increases heavily.d. vary continuously.[1]
4.Which of the following groups contain only biodegradable items?a. Grass, flowers and leatherb. Grass, wood and plasticc. Fruit-peels, cake and lime-juiced. Cake, wood and grass[1]
5.Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)a. massb. speedc. velocityd. momentum[1]
6.A solution turns red litmus blue, its pH is likely to bea. 1b. 4c. 5d. 10[1]
7.A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to bea. both concave.b. both convex.c. the mirror is concave and the lens is convex.d. the mirror is convex, but the lens is concave.[1]
8.No matter how far you stand from a mirror, your image appears erect. The mirror is likely to bea. only plane.b. only concave.c. only convex.d. either plane or convex.[1]
9.An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to bea. calciumb. carbonc. silicond. iron.[1]
10.Which of the following is not a part of the female reproductive system in human beings?a. Ovaryb. Uterusc. Vas deferensd. Fallopian tube[1]
11.Choose the correct option. The magnetic field inside a long straight solenoid-carrying currenta. is zero.b. decreases as we move towards its end.c. increases as we move towards its end.d. is the same at all points.[1]
12.The xylem in plants are responsible fora. transport of water.b. transport of food.c. transport of amino acids.d. transport of oxygen.[1]
13.The gap between two neurons is called aa. dendrite.b. synapse.c. axon.d. impulse.[1]
14.What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.a. Hydrogen gas and iron chloride are produced.b. Chlorine gas and iron hydroxide are produced.c. No reaction takes place.d. Iron salt and water are produced.[1]
15.Which of the following terms does not represent electrical power in a circuit?a. I²Rb. IR²c. VId. V²/R[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.Why do ionic compounds have high melting points?[2]
17.What are plant hormones?[2]
18.While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?[2]
19.How would you name the following compounds? (i) CH₃–CH₂–Br (ii) HCHO (iii) CH₃–CH₂–CH₂–CH₂–C≡CH[2]
20.A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?[2]
21.What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?[2]
22.Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?[2]
23.What is the difference between displacement and double displacement reactions? Write equations for these reactions.[2]
24.How are water and minerals transported in plants?[2]
25.What are the problems caused by the non-biodegradable wastes that we generate?[2]
26.What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?[2]
27.What are the methods used by plants to get rid of excretory products?[2]
28.Why is variation beneficial to the species but not necessarily for the individual?[2]
29.What are the advantages of sexual reproduction over asexual reproduction?[2]
30.The refractive index of diamond is 2.42. What is the meaning of this statement?[2]
31.Where do plants get each of the raw materials required for photosynthesis?[2]
32.How much energy is given to each coulomb of charge passing through a 6 V battery?[2]
33.Balance the following chemical equations. (a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O (b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O (c) NaCl + AgNO₃ → AgCl + NaNO₃ (d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl[2]
🔑 Show Answer Key — Set 3
- 1. (b) HCl
- 2. (d) Between the pole of the mirror and its principal focus.
- 3. (c) increases heavily.
- 4. (a), (c) and (d)
- 5. (c) velocity and (d) momentum
- 6. (d) 10
- 7. (a) both concave.
- 8. (d) either plane or convex.
- 9. (a) calcium
- 10. (c) Vas deferens
- 11. (d) is the same at all points.
- 12. (a) transport of water.
- 13. (b) synapse.
- 14. (a) Hydrogen gas and iron chloride are produced.
- 15. (b) IR²
- 16. Ionic compounds contain oppositely charged ions held together by strong electrostatic forces in a crystal lattice. A large amount of energy is required to overcome these forces, so they have high melting points.
- 17. Plant hormones are chemical substances produced in plants that coordinate growth, development and responses to stimuli. Examples include auxins, gibberellins, cytokinins and abscisic acid.
- 18. Dilution of concentrated acid is highly exothermic. If water is added to acid, the heat produced may cause the mixture to splash. Adding acid slowly to a larger volume of water lets the heat dissipate safely.
- 19. (i) Bromoethane. (ii) Methanal. (iii) Hex-1-yne.
- 20. No. This information alone is not enough to decide dominance. The father with blood group A must carry both A and O alleles (AO), while the mother is OO, so the daughter can be OO. To determine dominance, we need to know how alleles are expressed in heterozygous individuals; blood group A is expressed over O, but that cannot be concluded from only this family data.
- 21. Air contains a much higher concentration of oxygen than water. Therefore terrestrial organisms can obtain oxygen more easily than aquatic organisms, which must extract dissolved oxygen from water.
- 22. Soap molecules have hydrophilic ionic heads and hydrophobic hydrocarbon tails. In water, the tails avoid water and cluster inside while the heads face water, forming micelles. In ethanol, the hydrocarbon tails are also soluble, so micelles are not formed in the same way.
- 23. In a displacement reaction, a more reactive element displaces a less reactive element from its compound (an element and a compound react), e.g. Fe + CuSO₄ → FeSO₄ + Cu. In a double displacement reaction, two compounds react and exchange their ions (radicals) to form two new compounds, e.g. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl. So displacement involves one element replacing another, while double displacement involves an exchange of ions between two compounds.
- 24. Water and minerals are absorbed by root hairs and move into xylem vessels. They rise through xylem due to root pressure and mainly due to transpiration pull created by evaporation of water from leaves.
- 25. Non-biodegradable wastes persist in the environment, pollute soil and water, harm animals through ingestion or entanglement, and may enter food chains. Toxic non-biodegradable chemicals can accumulate and biomagnify, causing health problems in organisms.
- 26. The two properties are catenation and tetravalency. Catenation lets carbon form long chains, branched chains and rings with itself. Tetravalency lets carbon form four covalent bonds with carbon and other elements.
- 27. Plants remove wastes by diffusion of gases through stomata and lenticels, by storing wastes in leaves, bark or old xylem that later fall off, by converting wastes into resins and gums, and by excreting some substances into the surrounding soil.
- 28. Variation may or may not help a particular individual survive. But in a species, variations create diversity, so if the environment changes, some individuals may be better adapted and the species can survive.
- 29. Sexual reproduction combines genetic material from two parents and creates more variation among offspring. These variations improve the chances of survival of a species in changing environments and provide raw material for evolution.
- 30. It means that light travels 2.42 times faster in vacuum/air than in diamond. Equivalently, speed of light in diamond = (speed of light in vacuum)/2.42.
- 31. Plants get carbon dioxide from the air through stomata, water from the soil through roots, and sunlight from the Sun. Chlorophyll present in the leaves traps light energy.
- 32. Each coulomb of charge receives 6 J of energy.
- 33. (a) 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O (b) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O (c) NaCl + AgNO₃ → AgCl + NaNO₃ (d) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl