Quest4Learn
Sign in Start free

CBSE Class 10 Science 2026 — Paper 31(B)

80 marks · 3 hours · 39 questions (45 with the OR choices)

Take this paper as a timed mock

Free with an account: the board's time limit, marking at the end, and the answer to every question.

Sign up free Log in

Questions 1–9 · 1 mark each

  1. Q1 1 mark
    Select the gland that secretes digestive enzymes as well as hormones.
    1. (a)Thyroid
    2. (b)Pituitary
    3. (c)Pancreas
    4. (d)Adrenal
    Show answer
    (c) Pancreas
    Step-by-step solution →
  2. Q2 1 mark
    Choose the option that indicates the common structure between the basic filtration unit of kidneys and in the walls of alveoli of lungs.
    1. (a)Thin-walled veins poorly supplied with blood.
    2. (b)Thick-walled arteries richly supplied with blood.
    3. (c)A cluster of thin-walled capillaries richly supplied with blood.
    4. (d)Thick-walled capillaries poorly supplied with blood.
    Show answer
    (c) A cluster of thin-walled capillaries richly supplied with blood.
    Step-by-step solution →
  3. Q3 1 mark
    Given below a set of statements regarding blood circulation in humans. Identify the correct statement.
    1. (a)Oxygenated blood from lungs comes to the right auricle through pulmonary veins.
    2. (b)Vena cavas take oxygenated blood from body parts to right auricle.
    3. (c)Pulmonary artery takes oxygenated blood from heart to lungs.
    4. (d)Aorta takes oxygenated blood from heart to body parts.
    Show answer
    (d) Aorta takes oxygenated blood from heart to body parts.
    Step-by-step solution →
  4. Q4 1 mark
    Why do green plants occupy the first trophic level of any food chain ? Pick out the right option from the following.
    1. (a)They are fixed at one place in the soil so they cannot move from place to place.
    2. (b)They are widely distributed.
    3. (c)There are more herbivores than carnivores.
    4. (d)They have the ability to make food using sunlight, by photosynthesis.
    Show answer
    (d) They have the ability to make food using sunlight, by photosynthesis.
    Step-by-step solution →
  5. Q5 1 mark
    Decomposers play an important role in the nature. Which role do they not perform ?
    1. (a)Convert simple inorganic substances into complex organic substances using radiant energy of the Sun.
    2. (b)Act on the garbage and reduce it.
    3. (c)Natural replenishment of the soil.
    4. (d)Breakdown of complex organic matter of dead animals and plants into simple form.
    Show answer
    (a) Convert simple inorganic substances into complex organic substances using radiant energy of the Sun.
    Step-by-step solution →
  6. Q6 1 mark
    Round, green seeded pea plant (RRyy) was crossed with wrinkled, yellow seeded pea plant (rrYY), and progeny is produced. All plants of progeny will have :
    1. (a)round and green seeds
    2. (b)round and yellow seeds
    3. (c)wrinkled and green seeds
    4. (d)wrinkled and yellow seeds
    Show answer
    (b) round and yellow seeds
    Step-by-step solution →
  7. Q7 1 mark
    Select the option which illustrates the correct method of asexual reproduction in Spirogyra.
    1. (a)Budding
    2. (b)Regeneration
    3. (c)Fragmentation
    4. (d)Spore formation
    Show answer
    (c) Fragmentation
    Step-by-step solution →
  8. Q8 1 mark
    For Questions number 8 and 9, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Mammals and birds have efficient supply of oxygen to the body.

    Reason (R): Mammals and birds have four-chambered heart.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    Step-by-step solution →
  9. Q9 1 mark
    For Questions number 8 and 9, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Oxygen at the higher levels of the atmosphere is a product of UV radiation.

    Reason (R): At higher levels of the atmosphere, ozone shields the surface of the Earth from UV radiation from the Sun.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (d) Assertion (A) is false, but Reason (R) is true.
    Step-by-step solution →

Questions 10–12 · 2 marks each

  1. Q10 2 marks
    “The sex of the children in the human beings will be determined by what they inherit from their father.” Explain this statement.
    Show answer

    Every egg carries X, but a sperm carries X or Y, so the sex chromosome inherited from the father decides the child's sex.

    One of the twenty three pairs of human chromosomes is the sex-chromosome pair: a woman has and a man has . Because a gamete carries one chromosome of each pair, every egg the mother makes carries an X, while the father makes two kinds of sperm in equal numbers — half carrying X and half carrying Y. If an X carrying sperm fertilises the egg the child is , a girl; if a Y carrying sperm fertilises it the child is , a boy. The mother’s contribution is an X in either case, so the only thing that differs between a son and a daughter is the sex chromosome that came from the father — which is why the sex of the child is determined by what it inherits from its father.
    Step-by-step solution →
  2. Q11(a) 2 marks
    Electrical impulses are an excellent means to respond to stimuli in animal bodies. List any two limitations to the use of electrical impulses.
    Show answer

    Electrical impulses reach only cells connected by nervous tissue, and a cell needs time to reset before it can send another impulse.

    Two limitations are: (i) An electrical impulse reaches only those cells that are connected by nervous tissue, so it cannot reach every cell of the animal body; and (ii) after a cell has generated and transmitted an impulse it needs time to reset its mechanisms before it can send another, so impulses cannot be created and transmitted continuously. Because of these limits, animals also use chemical communication through hormones carried in the blood.
    Step-by-step solution →
    OR
    Q11(b) 2 marks
    Explain how the pea plant climbs up the support by means of tendrils.
    Show answer

    Unequal growth on the two sides makes the tendril curve round the support, so the pea plant climbs.

    Tendrils are thread-like outgrowths of the pea plant that are sensitive to touch. When a growing tendril comes into contact with a support, the part of the tendril in contact with the object does not grow as rapidly as the part away from the object. This unequal growth makes the tendril curve, so that it circles around the support and clings to it, and the weak stem of the pea plant is thereby held up and carried higher. Since the response is directional and is brought about by growth, it is a growth movement called thigmotropism.
    Step-by-step solution →
  3. Q12 2 marks
    Describe why do food chains generally consist of a few steps.
    Show answer

    Only about of energy passes to each next level, so after three or four steps too little remains to support another level.

    Food chains are short because the transfer of energy from one trophic level to the next is very wasteful. Only about of the energy present at a level is stored in the bodies of its organisms and so passed on; the other is used up in respiration, movement and maintaining body temperature, or leaves as undigested and excreted matter, and is finally lost as heat. So if the producers capture kJ, the herbivores get about kJ, the small carnivores about kJ and the large carnivores only about kJ. After three or four such transfers the energy left is too little to support a population at a further level, and since the flow of energy is unidirectional it can never be replaced. Food chains therefore generally consist of only three or four steps.
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks
    A tall pea plant (TT) is crossed with a dwarf pea plant (tt). Find out and progeny. Also mention the processes that lead to the formation of and progeny during the cross.
    Show answer

    is all tall (); has tall and dwarf plants in the ratio ; forms by cross-pollination, by self-pollination.

    progeny: every plant is and all of them are **tall**, because (tallness) is dominant over (dwarfness). progeny: , , and , that is a genotypic ratio of , giving tall and dwarf plants in the phenotypic ratio (three tall to one dwarf). Processes: the is formed by **cross-pollination** (cross-fertilisation) between the tall plant and the dwarf plant; the is formed by **self-pollination** of the () plants.
    Step-by-step solution →
  2. Q14 3 marks
    Name the organ that helps in the digestion of fats in human beings. Also describe its complete digestion into simple form. Where does absorption of food take place in the humans ?
    Show answer

    The liver's bile emulsifies fats, lipase then converts them to fatty acids and glycerol, and absorption takes place in the small intestine.

    Organ: the **liver**, which secretes bile juice (stored in the gall bladder and released into the small intestine). The pancreas, which secretes lipase, and the small intestine, where fat digestion is completed, also help in the digestion of fats. Complete digestion of fat: fats reach the small intestine as large globules. The bile salts of the bile juice break these large globules into many small droplets — emulsification — which greatly increases the surface available to the enzyme. The enzyme lipase, present in the pancreatic juice secreted by the pancreas and in the intestinal juice, then acts on this emulsified fat and breaks it down completely into its simple form, **fatty acids** and **glycerol**. Absorption: absorption of the digested food takes place in the **small intestine**, through the finger-like projections called villi in its inner lining, which give a large absorbing surface and are richly supplied with blood vessels that carry the absorbed food to every cell of the body.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks
    Read the following passage and answer the questions that follow : In many animals including humans, adrenaline hormone prepares for scary situation. The target organs on which it acts include the heart. The blood to the digestive system and skin is reduced, but the heart beats faster and breathing rate also increases. All these responses together enable the animal body to deal with such scary situation.
    1. (a)(i)Name the gland that secretes adrenaline hormone. How does it enable the animal body to deal with a scary situation ?[2]
    2. (a)(ii)OR : Why is the blood to the digestive system and skin reduced ?[2]
    3. (b)Why is it important for us to have iodised salt in our diet ?[1]
    4. (c)Why does a doctor advise some persons to take less sugar in their diet ?[1]
    Show answer

    Adrenal glands secrete adrenaline to prepare the body for danger; iodine is needed for thyroxine; diabetics must cut sugar because of low insulin.

    (a)(i) The **adrenal glands**, one above each kidney, secrete adrenaline. It is poured straight into the blood and carried to its target organs. It makes the heart beat faster, so more oxygen-rich blood reaches the muscles; it makes the smooth muscles around the small arteries of the digestive system and skin contract, so that blood is diverted from them to the skeletal muscles; and the breathing rate also increases, because of the contractions of the diaphragm and the rib muscles, so more oxygen is taken into the blood. Together these changes supply the skeletal muscles with the extra oxygen and glucose they need, and so enable the body to deal with the scary situation. OR (a)(ii) Because the smooth muscles around the small arteries supplying the digestive system and the skin contract and narrow them. Digestion and heat loss from the skin can wait in an emergency, so the blood saved there is diverted to the skeletal muscles, which need more oxygen and glucose to act quickly. (b) Iodine is needed by the thyroid gland to make the hormone thyroxine, which regulates carbohydrate, protein and fat metabolism. Too little iodine in the diet means too little thyroxine, and the person suffers from goitre, with a swollen neck; iodised salt supplies the iodine. (c) Because such persons are diabetic: their pancreas does not secrete enough insulin, the hormone that lowers blood sugar, so the sugar they eat keeps the blood sugar level high. Taking less sugar keeps that level within what their weakened control can manage.
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks
    1. (i)Sugarcane and roses are mostly grown by vegetative propagation. Define this mode of reproduction.
    2. (ii)List two advantages of vegetative propagation.
    3. (iii)Distinguish between unisexual and bisexual flowers. Give one example of each kind.
    Show answer

    Vegetative propagation raises plants from vegetative parts; its advantages are earlier flowering and seedless plants; unisexual flowers have one whorl, bisexual flowers both.

    (i) Vegetative propagation is the mode of **asexual** reproduction in plants in which new plants are produced from the vegetative parts of a plant — the root, stem, leaf or a bud — without the involvement of gametes, fertilisation or seeds. Since only one parent is involved, the new plants are genetically identical to it. (ii) Any two: plants raised in this way bear flowers and fruits **earlier** than those grown from seeds; plants such as banana, orange, rose and jasmine, which have lost the capacity to produce viable seeds, can still be grown; and every plant produced is genetically identical to the parent, so a desirable variety is preserved unchanged. (iii) A **unisexual** flower contains only one reproductive whorl — either the stamens or the pistil — so it can be cross-pollinated only; a **bisexual** flower contains both the stamens and the pistil in the same flower, so it may be self-pollinated as well. Example of a unisexual flower: papaya (also watermelon). Example of a bisexual flower: Hibiscus or China rose (also mustard).
    Step-by-step solution →
    OR
    Q16(b) 5 marks
    1. (i)Differentiate between self-pollination and cross-pollination. (two points)
    2. (ii)Explain how does pollination lead to fertilisation in flowering plants.
    3. (iii)Name the end-products of sexual reproduction in plants.
    Show answer

    Self-pollination is within the same flower, cross-pollination between flowers; the pollen tube enables fertilisation, and the end-products are the seed and fruit.

    (i) In self-pollination the pollen is transferred from the anther to the stigma of the **same** flower, whereas in cross-pollination it is transferred from one flower to **another** flower. Self-pollination may or may not need a pollinating agent, whereas cross-pollination always needs an agent — wind, water or an animal such as an insect or bird. (ii) Pollination only places the pollen grain on the stigma. There the grain germinates and puts out a pollen tube, which grows down through the style, reaches the ovary and enters an ovule, carrying the male germ cell with it. Inside the ovule that male gamete fuses with the female gamete (the egg), and this fusion is fertilisation; it produces the zygote. So pollination leads to fertilisation through the growth of the pollen tube, and the two events are not the same. (iii) The zygote grows into the **embryo**, the ovule becomes the **seed** and the ovary becomes the **fruit**. The end-products of sexual reproduction in plants are therefore the seed, containing the embryo, and the fruit.
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark
    Which of the following is not an exothermic reaction ?
    1. (a)Decomposition of vegetable matter into compost
    2. (b)Reaction of water with quick lime
    3. (c)Respiration process taking place in the cells of our body
    4. (d)Decomposition of calcium carbonate to calcium oxide and carbon dioxide
    Show answer
    (d) Decomposition of calcium carbonate to calcium oxide and carbon dioxide
    Step-by-step solution →
  2. Q18 1 mark
    Electrolysis of water is an example of :
    1. (a)thermal decomposition reaction
    2. (b)photochemical decomposition reaction
    3. (c)double-displacement reaction
    4. (d)electrolytic decomposition reaction
    Show answer
    (d) electrolytic decomposition reaction
    Step-by-step solution →
  3. Q19 1 mark
    The acid presents in nettle sting is :
    1. (a)Tartaric acid
    2. (b)Oxalic acid
    3. (c)Methanoic acid
    4. (d)Acetic acid
    Show answer
    (c) Methanoic acid
    Step-by-step solution →
  4. Q20 1 mark
    Which one of the following non-metals exists as liquid at room temperature ?
    1. (a)Bromine
    2. (b)Sulphur
    3. (c)Iodine
    4. (d)Chlorine
    Show answer
    (a) Bromine
    Step-by-step solution →
  5. Q21 1 mark
    Which one among the following alloys has mercury as one of its constituents ?
    1. (a)Stainless steel
    2. (b)Brass
    3. (c)Zinc amalgam
    4. (d)Bronze
    Show answer
    (c) Zinc amalgam
    Step-by-step solution →
  6. Q22 1 mark
    When ethanoic acid is treated with sodium hydrogen carbonate, the gas evolved is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (a)
    Step-by-step solution →
  7. Q23 1 mark
    The second member of alkyne homologous series is :
    1. (a)propene
    2. (b)ethyne
    3. (c)ethene
    4. (d)propyne
    Show answer
    (d) propyne
    Step-by-step solution →
  8. Q24 1 mark
    For Question number 24, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): It is advised that while diluting a concentrated acid, acid should be added slowly to water and not water to acid.

    Reason (R): The process of dissolving an acid in water is endothermic.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (c) Assertion (A) is true, but Reason (R) is false.
    Step-by-step solution →

Question 25 · 2 marks

  1. Q25 2 marks
    Give reasons for the following :
    1. (a)Dry HCl gas does not change the colour of a dry blue litmus paper.
    2. (b)Copper sulphate crystals turn white on heating.
    Show answer

    Dry HCl gas has no water, so it forms no ions; heating blue drives off its water, leaving white .

    (a) Dry HCl gas contains no water, so it does not ionise and releases no hydrogen ions; a substance shows acidic behaviour, including its action on litmus, only through the ions it produces in water. With no water in the gas and none in the paper, dry blue litmus stays blue. Moist blue litmus paper turns red with the same gas, because the moisture lets it ionise. (b) Blue copper sulphate crystals are hydrated copper sulphate, , and the five molecules of water of crystallisation are what give them their blue colour. On heating, this water is driven off as vapour and white anhydrous copper sulphate, , is left behind: . Adding water to the white powder turns it blue again.
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26 3 marks
    What happens when :
    1. (a)silver chloride is kept in sunlight ?
    2. (b)lead nitrate solution is added to potassium iodide solution ?
    3. (c)food materials containing fats and oils are left for a long time ?
    Show answer

    Silver chloride turns grey in sunlight, lead nitrate and potassium iodide give yellow lead iodide, and fats and oils turn rancid.

    (a) The white silver chloride turns grey. Sunlight decomposes it into silver and chlorine, , and the grey colour is the silver metal set free. This is a photochemical decomposition reaction. (b) A bright yellow precipitate of lead iodide is formed at once: . This is a double displacement (precipitation) reaction, the potassium nitrate staying in solution. (c) The food becomes rancid. The fats and oils are slowly oxidised by the oxygen of the air, so the smell and the taste of the food turn unpleasant. Rancidity is delayed by adding antioxidants, by using airtight containers, by flushing the packet with nitrogen and by refrigeration.
    Step-by-step solution →
  2. Q27(a) 3 marks
    During electrolysis of brine solution, a gas (A) is liberated at the anode. When the gas (A) is passed through slaked lime, a compound (B) is formed which is used for disinfecting drinking water.
    1. (i)Write the names of (A) and (B).
    2. (ii)Write the chemical equation involved.
    3. (iii)Write one use of compound (B) other than disinfecting water.
    Show answer

    A is chlorine and B is bleaching powder, ; B is also used to bleach cotton and linen in the textile industry.

    (i) (A) is chlorine, , the gas liberated at the anode during the electrolysis of brine; (B) is bleaching powder, calcium oxychloride, . (ii) (iii) Bleaching powder is used for bleaching cotton and linen in the textile industry. It is also used for bleaching wood pulp in paper factories and as an oxidising agent in many chemical industries.
    Step-by-step solution →
    OR
    Q27(b) 3 marks
    Define the following terms with an example :
    1. (i)Olfactory indicators
    2. (ii)Water of crystallisation
    3. (iii)Basic salt
    Show answer

    Olfactory indicators change smell (onion); water of crystallisation is fixed water in the crystal; a basic salt comes from a strong base and weak acid.

    (i) An olfactory indicator is a substance whose smell changes, or is lost, in acidic and basic solutions, so it tells an acid from a base by odour instead of by colour. Example: onion - a cloth strip carrying the onion smell keeps it with dilute but loses it with dilute (vanilla essence and clove oil behave the same way). (ii) Water of crystallisation is the fixed number of water molecules chemically combined with one formula unit of a salt in its crystal. Example: copper sulphate crystals, (blue vitriol), which carry five such molecules and turn white on heating. (iii) A basic salt is the salt of a strong base and a weak acid; its aqueous solution has pH greater than and turns red litmus blue. Example: sodium carbonate, (pH about ), formed from and the weak acid .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks
    Read the following passage and answer the questions that follow : When metals are burnt in air, they form oxides. Metal oxides are generally basic in nature. But some metal oxides show both acidic as well as basic behaviour. Most metal oxides are insoluble in water, but some of these dissolve in water to form alkalis. Different metals show different reactivities towards oxygen. Metals such as sodium and potassium react vigorously whereas metals like silver and gold do not react with oxygen even at high temperature.
    1. (a)Why are metals like sodium and potassium kept immersed in kerosene oil ?[1]
    2. (b)Why does copper metal turn black on heating ?[1]
    3. (c)(i)What are the amphoteric oxides ? Give two examples.[2]
    4. (c)(ii)OR : (I) Name a water soluble metal oxide. Write the chemical equation for its reaction with water. (II) Why do silver and gold not react with oxygen even at high temperature ?[2]
    Show answer

    Kerosene keeps air and water away from reactive sodium and potassium; copper forms black copper oxide; amphoteric oxides react with both acids and bases.

    (a) Sodium and potassium are so reactive that they react with the oxygen and the moisture of air at room temperature, and the heat released can set the metal on fire. Kerosene oil does not react with them and keeps air and water vapour away, so the metals are stored immersed in it. (b) On heating, copper combines with the oxygen of air and a black layer of copper(II) oxide forms on its surface: (black). (c)(i) Amphoteric oxides are metal oxides that react with both acids and bases to give a salt and water, that is, they show basic as well as acidic behaviour. Examples: aluminium oxide and zinc oxide . OR : (c)(ii)(I) Sodium oxide, , is soluble in water and gives an alkali: (potassium oxide behaves the same way). (II) Silver and gold are the least reactive metals, at the bottom of the reactivity series; they hold their outer electrons so firmly that they do not give them up to oxygen, so no oxide forms even at high temperature and both are found in the free state.
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks
    1. (i)Define catenation. Why does carbon show catenation ?
    2. (ii)Define homologous series. Give examples of two homologues whose molecular mass differ by 14 amu.
    3. (iii)Why do soaps not work well in hard water ?
    Show answer

    Carbon is tetravalent with strong bonds; methane and ethane differ by 14 u; soap forms insoluble scum in hard water.

    (i) Catenation is the property of an element whose atoms link with one another by covalent bonds to form long straight chains, branched chains and closed rings. Carbon shows it because it is tetravalent - four valence electrons, so four covalent bonds per atom - and because the carbon atom is small, which makes the C to C bond short and very strong (about kJ mol), so long chains remain stable. (ii) A homologous series is a series of organic compounds with the same general formula and similar chemical properties in which successive members differ by one group, that is by u. Example of two such homologues: methane ( u) and ethane ( u), since u. (iii) Hard water contains dissolved calcium and magnesium salts. Their and ions react with the soap to form insoluble calcium and magnesium salts of the fatty acid - a curdy white scum - so the soap is used up instead of forming lather and cleans poorly: .
    Step-by-step solution →
    OR
    Q29(b) 5 marks
    1. (i)Why do covalent compounds have low melting and boiling points ?
    2. (ii)Name the reagent that can convert ethanol to ethanoic acid.
    3. (iii)Why is ethanoic acid a weaker acid than mineral acids ?
    4. (iv)Define esterification reaction.
    5. (v)What are ‘Micelles’ ?
    Show answer

    Weak forces between molecules give low melting and boiling points; alkaline oxidises ethanol; ethanoic acid ionises partially; micelles are clusters of soap molecules.

    (i) Within a molecule the atoms are held by strong covalent bonds, but the forces of attraction **between** molecules are weak. Melting and boiling only separate whole molecules from one another, so only these weak intermolecular forces have to be overcome and very little heat energy is needed - hence the low melting and boiling points. (ii) Alkaline potassium permanganate ( with or , warmed); acidified potassium dichromate ( with ) is equally acceptable. Both are oxidising agents: . (iii) Because ethanoic acid ionises only partially in water: . A mineral acid such as ionises almost completely, so at the same concentration it gives many more hydrogen ions; fewer ions means a weaker acid. (iv) Esterification is the reaction of a carboxylic acid with an alcohol, in the presence of a few drops of concentrated sulphuric acid as catalyst, to give a sweet-smelling ester and water: . (v) Micelles are the spherical clusters into which soap molecules gather in water, with the hydrophobic hydrocarbon tails pointing inwards towards the oily dirt and the hydrophilic ends pointing outwards into the water. They hold the dirt suspended as an emulsion so that it can be rinsed away.
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark
    Work done in displacing an electron between two points having potential difference of 1 V, is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (b)
    Step-by-step solution →
  2. Q31 1 mark
    Angle of deviation in refraction of light through a glass prism is the :
    1. (a)Angle between the normal at the face on the emerging side of the prism and the emergent ray.
    2. (b)Angle between the normal at the face on the emerging side of the prism and the incident ray.
    3. (c)Angle between the incident ray and the refracted ray.
    4. (d)Angle between the directions of incident ray and emergent ray.
    Show answer
    (d) Angle between the directions of incident ray and emergent ray.
    Step-by-step solution →
  3. Q32 1 mark
    For Question number 32, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): When light passes from one medium to another medium, the speed of light may increase or decrease.

    Reason (R): Refractive index of one medium with respect to the other medium may be greater or less than 1.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    Step-by-step solution →

Questions 33–34 · 2 marks each

  1. Q33 2 marks
    Write any two differences between the images formed by convex mirror and plane mirror.
    Show answer

    The plane mirror image is the same size as the object; the convex mirror image is diminished and lies between P and F.

    Any two of the following: (1) Size: the image formed by a plane mirror is of the same size as the object (), whereas the image formed by a convex mirror is diminished, smaller than the object (). (2) Position: the image formed by a plane mirror is as far behind the mirror as the object is in front of it, whereas the image formed by a convex mirror lies behind the mirror between the pole P and the focus F, nearer to the mirror than the object is. (3) Dependence on object distance: the plane mirror image stays the same size wherever the object is, whereas the convex mirror image becomes smaller as the object moves away from the mirror. (Both images are virtual and erect, so those are not differences.)
    Step-by-step solution →
  2. Q34(a) 2 marks
    Name the phenomenon due to which a prism splits the incident white light into a band of colours. State the reason of the phenomenon also.
    Show answer

    Dispersion: white light is a mixture of seven colours, and glass has a different refractive index for each, so they bend differently.

    The phenomenon is dispersion of white light. Reason: white light is a mixture of seven colours (VIBGYOR). Each colour travels with a different speed in glass, so the refractive index of glass is different for different colours. On refraction through the prism the different colours are therefore bent through different angles with respect to the incident ray: red is bent the least and violet the most. The colours emerge along different paths and form a band of colours, the spectrum.
    Step-by-step solution →
    OR
    Q34(b) 2 marks
    When a ray of light passes from water to air (I) will the angle of refraction in air () be greater than the angle of incidence in water () or less than it ? (II) and when we increase the angle of incidence in water, will the angle of refraction in air increase or decrease ? What is the limiting value for ?
    Show answer

    The angle of refraction in air is greater than , it increases with , and its limiting value is .

    (I) The angle of refraction in air is greater than the angle of incidence in water (), because the ray passes from an optically denser medium (water) into a rarer one (air), speeds up and bends away from the normal. (II) When the angle of incidence in water is increased, the angle of refraction in air also increases (faster than , since ). The limiting value of is : the refracted ray then grazes along the water surface, which for water happens at .
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks
    1. (a)Explain the Tyndall effect with the help of one suitable example.
    2. (b)What happens when a white light gets scattered from (i) very fine particles (ii) larger size particles ?
    Show answer

    Tyndall effect is scattering of light by colloidal particles, as in a smoke-filled room; very fine particles scatter mainly blue, larger ones longer wavelengths.

    (a) Tyndall effect: when a beam of light passes through a medium containing very small suspended (colloidal) particles, the particles scatter the light in all directions, and the path of the beam becomes visible. Example: when a fine beam of sunlight enters a smoke-filled room through a small hole, its path is seen because the smoke particles scatter the light. (Sunlight passing through the canopy of a dense forest is seen as shafts because the mist droplets scatter it.) (b) The colour of the scattered light depends on the size of the particles. (i) Very fine particles, such as air molecules, scatter mainly blue light (the shorter wavelengths), so the scattered light looks blue; this is why the clear sky is blue. (ii) Larger particles scatter light of longer wavelengths, so red light (light of longer wavelength) is seen in the scattered light. If the particles are large enough, such as the water droplets in clouds, all colours are scattered about equally and the scattered light may even appear white.
    Step-by-step solution →
  2. Q36 3 marks
    By using the data given in the table, compare the properties of images formed by convex lens and concave mirror in terms of the positions and nature of images formed.
    Optical deviceObject distance (cm)Focal length (cm)Height of object (cm)
    Convex lens20106
    Concave mirror30106
    Show answer

    Both images are real and inverted, but the lens image is the same size and the mirror image half-size.

    Convex lens ( cm, cm): cm and . The image is formed cm from the lens on the other side, at . It is real, inverted and of the same size as the object ( cm). Concave mirror ( cm, cm): cm and . The image is formed cm in front of the mirror, on the same side as the object, between F and C. It is real, inverted and diminished ( cm). Comparison: both images are real and inverted, but the lens forms its image on the side opposite the object and of the same size, while the mirror forms its image on the object's side and half the size of the object.
    Step-by-step solution →
  3. Q37 3 marks
    State the role of fuse and earthing in domestic electric circuit. Suggest any two precautions to be taken to avoid electrical accidents.
    Show answer

    A fuse breaks the circuit when current exceeds the safe value; earthing prevents electric shock from a faulty metal-bodied appliance.

    Role of fuse: a fuse is a safety device connected in series with the live wire. Its wire has a low melting point, so when the current rises above the safe (rated) value, because of overloading or a short circuit, the wire heats up, melts and breaks the circuit. This stops the current and protects the appliances and the wiring from damage and fire. Role of earthing: the metal body of an appliance is connected through the earth wire to a metal plate buried deep in the ground. If the live wire touches the metal body because of a fault, the current flows through this low-resistance path into the earth, the body stays at earth potential, and a person touching the appliance does not get a severe electric shock. Precautions (any two): (1) Do not overload a socket by connecting too many appliances to it. (2) Use a fuse or MCB of the correct rating. (3) Never touch switches or appliances with wet hands. (4) Use earthed three-pin plugs for appliances with metal bodies, and replace damaged or poorly insulated wires.
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks
    Read the following passage and answer the questions that follow : H.C. Oersted demonstrated that every current-carrying wire produces magnetic field around it. The pattern of the magnetic field depends upon the geometrical structure the current carrying wire is folded into. When a current-carrying wire is kept in a magnetic field, it experiences a force. Magnitude of this force is maximum when direction of magnetic field is at right angles to the current-carrying wire. Some rules to determine the direction of magnetic field and force were given by scientists Maxwell and Fleming.
    1. (a)What is the direction of magnetic field inside and outside a solenoid ?[1]
    2. (b)Same electric current is flowing through three identical wires A, B and C. If wires A, B and C are making respectively angles , and with the magnetic field, which of the wires will experience maximum force and why ?[1]
    3. (c)(i)Name and state the law which is required to find out the direction of force acting on a current carrying wire, kept in a magnetic field.[2]
    4. (c)(ii)OR : Name and state the law which is required to find out the direction of magnetic field around the current carrying straight conductor.[2]
    Show answer

    Inside a solenoid the field is uniform; wire C feels maximum force at ; Fleming's left-hand rule gives force direction; OR right-hand thumb rule.

    (a) Inside the solenoid the magnetic field lines are parallel straight lines running from the south-pole end to the north-pole end, so the field inside is uniform; outside, they run from the north-pole end round to the south-pole end, as for a bar magnet, and the lines form closed loops. (b) Wire C experiences the maximum force. The force is largest when the wire is at right angles to the magnetic field, and a wire making with the field is at right angles to it (a turn is a turn the other way); A and B, at and , are not. Since , the forces are in the ratio . (c)(i) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points along the magnetic field and the middle finger along the current, the thumb gives the direction of the force (motion) on the conductor. OR : (c)(ii) Right-hand thumb rule (Maxwell's corkscrew rule): hold the straight conductor in the right hand with the thumb pointing along the current; the direction in which the fingers wrap around the conductor gives the direction of the magnetic field lines, which are concentric circles.
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)In a house, 5 fans, rated 100 W; 220 V each are used for 4 hours daily and an electric heater rated 1000 W; 220 V is used for 5 hours daily. Calculate the cost of electrical energy consumed by the fans and the electric heater in a month of 30 days if the cost of 1 unit of electrical energy is ₹ 5.
    2. (ii)You have two fuse wires X and Y with electric current rating 5 A and 10 A respectively. Which of the two would you use with a heater rated 2000 W; 220 V ? Justify your answer.
    Show answer

    The fans and heater use 210 kWh a month costing ₹ 1050; fuse Y (10 A) suits the heater, which draws about 9.09 A.

    (i) Power of the five fans W kW; power of the heater W kW. Energy per day: fans kWh, heater kWh, total kWh. Energy in 30 days kWh units (fans units, heater units). Cost units at ₹ 5 per unit ₹ 1050 (fans ₹ 300, heater ₹ 750). (ii) Fuse wire Y ( A). The heater draws A. This is more than the A rating of X, so X would melt as soon as the heater is switched on; it is less than the A rating of Y, so Y carries the normal current and melts only if the current exceeds A, which protects the circuit from overloading and short-circuiting.
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)State the relationship of the resistance () of a wire with its area of cross-section () and its length (). With the help of this relation, define resistivity of the material of the wire.
    2. (ii)In an electric circuit, 2 A electric current flows through a resistor for 50 seconds. (I) Calculate the heat produced in the wire. (II) If another resistor is connected in parallel to the given resistor, calculate the heat produced in the circuit in 50 seconds.
    Show answer

    Resistivity is the resistance of a wire of unit length and unit area; heat is 8000 J, rising to 16000 J in parallel.

    (i) For a wire of a given material at a given temperature, the resistance is directly proportional to its length and inversely proportional to its area of cross-section: and , so , where is the resistivity of the material. Putting m and m gives : the resistivity of a material is the resistance of a wire of that material of unit length and unit area of cross-section. Its SI unit is the ohm metre ( m). (ii) (I) J. (II) The same supply keeps the potential difference V across the resistors. In parallel, , so ; the supply now delivers A ( A through each resistor), and J, twice the heat in (I).
    Step-by-step solution →

Other 2026 papers

All CBSE Class 10 Science papers →