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CBSE Class 10 Science 2026 — Paper 31/3/3

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

32 of its 45 questions also appear in 31/3/1, 31/3/2 and other papers; 13 are only in this paper.

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Questions 1–9 · 1 mark each

  1. Q1 1 mark

    Also in 31/3/1 (Q7), 31/3/2 (Q4)

    The growth of tendrils in grapes plants is due to :
    1. (a)Effect of light
    2. (b)Effect of gravity
    3. (c)Rapid cell division in tendril cells in contact with the support
    4. (d)Rapid cell division in tendril cells that are away from the support
    Show answer
    (d) Rapid cell division in tendril cells that are away from the support
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/3/1 (Q1)

    Pravin was given a list of characteristics associated with the process of anaerobic respiration in humans, in the table given below : Which of the above characteristics is/are related to the above process ?
    LocationConditionEnd Product
    Characteristic(i) Muscle Cell(ii) Requires presence of Oxygen (O₂) and Carbon dioxide (CO₂)(iii) 3-Carbon molecules
    1. (a)(i) and (ii)
    2. (b)(i) and (iii)
    3. (c)(ii) and (iii)
    4. (d)(i) only
    Show answer
    (b) (i) and (iii)
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/3/1 (Q5), 31/3/2 (Q2)

    Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level form the :
    1. (a)Food web
    2. (b)Ecosystem
    3. (c)Ecological pyramid
    4. (d)Food chain
    Show answer
    (a) Food web
    Step-by-step solution →
  4. Q4 1 mark

    Also in 31/3/1 (Q2), 31/3/2 (Q1)

    Observe the figure given below and identify the incorrect step for the activity set-up :
    Bell-jar Watch-glass containing potassium hydroxide (I) (II)
    1. (a)Both plants are kept in the dark room for three days before placing them in separate glass jars.
    2. (b)Both plants are covered with separate wooden bell-jars.
    3. (c)Use vaseline to seal the bottom of the jars with the glass plates.
    4. (d)Both potted plants were kept in sunlight for a few hours before the iodine test for the presence of starch.
    Show answer
    (b) Both plants are covered with separate wooden bell-jars.
    Step-by-step solution →
  5. Q5 1 mark

    Also in 31/3/1 (Q6), 31/3/2 (Q5)

    In accumulation of toxic substances at higher trophic levels of an ecosystem through the food chain, which of the following organisms is affected the most ?
    1. (a)Small aquatic plants
    2. (b)Human beings
    3. (c)Small fish
    4. (d)Large fish
    Show answer
    (b) Human beings
    Step-by-step solution →
  6. Q6 1 mark
    Which of the following represents the correct sequence of events of sexual reproduction in a flower ?
    1. (a)Pollination, Fertilization, Seed, Embryo
    2. (b)Seed, Embryo, Fertilization, Pollination
    3. (c)Seed, Plant, Flower, Pollination, Fertilization
    4. (d)Pollination, Fertilization, Embryo, Seed
    Show answer
    (d) Pollination, Fertilization, Embryo, Seed
    Step-by-step solution →
  7. Q7 1 mark
    The sexually transmitted disease caused by bacteria is :
    1. (a)Diarrhoea
    2. (b)AIDS
    3. (c)Gonorrhoea
    4. (d)Wart
    Show answer
    (c) Gonorrhoea
    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): Arteries have valves as they have to withstand high pressure.

    Reason (R): Arteries are vessels which carry blood away from the heart to various organs.

    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 →
  9. Q9 1 mark

    Also in 31/3/1 (Q8)

    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): Natural replenishment of soil will not take place in absence of microbes.

    Reason (R): Microbes, comprising of bacteria and fungi, break down dead remains and waste products of organisms, and they go into the soil.

    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 10–12 · 2 marks each

  1. Q10 2 marks
    What are hormones ? State any one function of the following hormones :
    1. (i)Insulin
    2. (ii)Adrenaline
    Show answer

    Hormones are chemical messengers secreted into the blood; insulin lowers blood sugar and adrenaline makes the heart beat faster in an emergency.

    Hormones are chemical messengers secreted in small amounts by endocrine (ductless) glands directly into the blood, which carries them to target organs, where they control and coordinate particular activities of the body. (i) Insulin, secreted by the pancreas, regulates the blood sugar level: it lowers a raised level by helping cells take up glucose (too little insulin causes diabetes). (ii) Adrenaline, secreted by the adrenal glands, prepares the body for dealing with stress or an emergency: it makes the heart beat faster so that more oxygen reaches the muscles.
    Step-by-step solution →
  2. Q11 2 marks

    Also in 31/3/1 (Q10)

    1. (i)Chlorofluorocarbons (CFCs) have been linked to depletion of ozone layer. In 1987, the United Nations Environment Programme (UNEP) succeeded in making an agreement. State this agreement.
    2. (ii)What is the role of ozone in our atmosphere ?
    Show answer

    UNEP's 1987 Montreal Protocol froze CFC production at 1986 levels; ozone shields the Earth from harmful UV radiation.

    (i) In 1987 the United Nations Environment Programme (UNEP) forged an agreement to freeze the production of CFCs at 1986 levels; it is known as the Montreal Protocol. (ii) Ozone () at the higher levels of the atmosphere shields the surface of the Earth from the harmful ultraviolet (UV) radiation of the Sun, which is highly damaging to organisms and causes skin cancer in human beings; the ozone layer thus protects life on Earth.
    Step-by-step solution →
  3. Q12 2 marks

    Also in 31/3/1 (Q11), 31/3/2 (Q10)

    What kind of respiration provides more energy and why ?
    Show answer

    Aerobic respiration gives more energy because it breaks glucose down completely with oxygen, whereas anaerobic respiration breaks it down only partially.

    Aerobic respiration provides more energy. In aerobic respiration glucose is broken down completely, in the presence of oxygen in the mitochondria, into carbon dioxide and water, so all the energy respiration can obtain from it is released (up to about 38 ATP per glucose molecule). In anaerobic respiration, without oxygen, glucose is broken down only partially, into ethanol and carbon dioxide in yeast or lactic acid in muscle cells, so much of its energy stays locked in these products and only 2 ATP are formed.
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks

    Also in 31/3/1 (Q14)

    Show the cross and observations made by Mendel when he crossed pure tall pea plant with a pure short pea plant to get progeny.
    Show answer

    The cross gives all-tall plants in ; tallness is dominant, shortness is recessive, and the traits do not blend.

    Cross: Parents: pure tall () pure short (). Gametes: from the tall parent and from the short parent. progeny: , all tall. Observations: (1) All the plants were tall. (2) No plant was short or of medium height, so the traits did not blend. (3) Only one parental trait, tallness, was expressed: tallness is dominant and shortness is recessive (present but hidden in the ).
    Step-by-step solution →
  2. Q14 3 marks
    Give reasons for the following :
    1. (a)Herbivores have a longer small intestine.
    2. (b)Inner lining of small intestine has numerous finger-like projections.
    3. (c)Rate of breathing in aquatic organisms is much faster than that in terrestrial organisms.
    Show answer

    Herbivores need time to digest cellulose; villi increase absorbing surface; water holds less oxygen than air, so aquatic organisms breathe faster.

    (a) Herbivores eat plant food rich in cellulose, which takes a long time to digest; a longer small intestine holds the food for longer and gives the cellulose the time it needs to be digested. (b) The finger-like projections are villi. They increase the surface area for the absorption of digested food, and they are richly supplied with blood vessels that carry the absorbed food to all parts of the body. (c) Water holds far less dissolved oxygen than the same volume of air, so aquatic organisms must pass much more water over their gills, and therefore breathe much faster, to obtain the oxygen they need.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15(a) 4 marks

    Also in 31/3/1 (Q15(a)), 31/3/2 (Q15(a))

    Read the following passage and answer the questions that follow : Not all plants carry out photosynthesis by the same mechanism. In most plants, it depends directly on gaseous carbon dioxide that diffuses into the leaf. However, some plants can store carbon dioxide in the vacuole of the leaf cells as part of a complex carbon compound. This compound is transported to the chloroplast and releases carbon dioxide when required for photosynthesis. This special mechanism is believed to have evolved as an adaptation in such plants which do not open stomata during the daytime to conserve water for survival in dry conditions (desert conditions).
    1. (i)Which process in these plants is minimised to help the plants survive in dry conditions ?
    2. (ii)Which part of the leaf is responsible for exchange of gases during photosynthesis ?
    Show answer

    Transpiration is minimised because the stomata stay closed by day; gas exchange in photosynthesis takes place through the stomata.

    (i) Transpiration, the loss of water as vapour through the stomata: by keeping their stomata closed during the day, these plants minimise it and conserve water. (ii) The stomata, tiny pores in the epidermis of the leaf, each surrounded by two guard cells: carbon dioxide enters and oxygen leaves through them during photosynthesis.
    Step-by-step solution →
    OR
    Q15(b) 4 marks

    Also in 31/3/1 (Q15(b)), 31/3/2 (Q15(b))

    Read the following passage and answer the questions that follow : Not all plants carry out photosynthesis by the same mechanism. In most plants, it depends directly on gaseous carbon dioxide that diffuses into the leaf. However, some plants can store carbon dioxide in the vacuole of the leaf cells as part of a complex carbon compound. This compound is transported to the chloroplast and releases carbon dioxide when required for photosynthesis. This special mechanism is believed to have evolved as an adaptation in such plants which do not open stomata during the daytime to conserve water for survival in dry conditions (desert conditions).
    1. (i)List the events that occur during the process of photosynthesis.
    2. (ii)When are such desert plants likely to take in carbon dioxide from the environment, unlike other plants ?
    3. (iii)Draw a labelled diagram of stomata with open stomatal pore.
    Show answer

    Photosynthesis: light absorbed, water split, carbon dioxide reduced; desert plants take in carbon dioxide at night; stomata have guard cells around the pore.

    (i) The events are: (1) absorption of light energy by chlorophyll; (2) conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen; (3) reduction of carbon dioxide to carbohydrates. (ii) At night: these plants keep their stomata closed during the day, so they open them at night, take in carbon dioxide and store it as an intermediate compound, which is used for photosynthesis during the day. (iii) The diagram shows two bean-shaped guard cells, each with a nucleus, chloroplasts and a thick inner wall, around an open stomatal pore, with epidermal cells around them (see the labelled diagram).
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks

    Also in 31/3/1 (Q16(a)), 31/3/2 (Q16(b))

    Observe the given diagram and answer the questions that follow :
    1. (i)Give the name of the structure and type of reproduction shown in the above diagram.
    2. (ii)State one advantage and one disadvantage of the above mentioned method of reproduction.
    3. (iii)Give reason : Asexual reproduction lacks genetic variation.
    4. (iv)Why have higher organisms resorted to sexual reproduction in spite of its complexity ?
    Adventitious bud Young Plant Marginal notch Leaf
    Show answer

    Bryophyllum leaf buds show vegetative propagation; asexual reproduction gives identical offspring, whereas sexual reproduction gives variation that helps survival and evolution.

    (i) The structure is the leaf of Bryophyllum, with adventitious buds in the notches of its margin; the type of reproduction is vegetative propagation, a form of asexual reproduction. (ii) Advantage: the new plants are genetically similar to the parent, so all its characters are kept, and many plants are raised quickly (they also flower and fruit earlier than plants grown from seeds). Disadvantage: the offspring show no variation, so they cannot adapt if the environment changes, and one disease can destroy all of them. (iii) Only one parent is involved and there is no fusion of gametes; each offspring receives a copy of the parent's DNA made during cell division, so apart from tiny copying errors it is genetically identical to the parent. (iv) Sexual reproduction combines DNA from two parents through gametes that each carry half the DNA, so every offspring has a new combination of characters. This variation helps the species survive changes in the environment and is the basis of evolution, which outweighs the complexity of the process.
    Step-by-step solution →
    OR
    Q16(b) 5 marks

    Also in 31/3/1 (Q16(b)), 31/3/2 (Q16(a))

    Observe the given diagram and answer the questions that follow :
    1. (i)Give the name and type of reproduction shown in the above diagram.
    2. (ii)Comment on the processes taking place in stage P.
    3. (iii)Name an organism which reproduces by the above mentioned method.
    4. (iv)Name the method that can be used to raise plants that have lost their capacity to produce seeds. List any two advantages of growing plants by such a method.
    Nucleus Cytoplasm Cell Cyst (Protective wall) P
    Show answer

    Multiple fission (asexual) occurs in Plasmodium; vegetative propagation raises plants that cannot make seeds, giving earlier flowering and genetically similar plants.

    (i) The diagram shows multiple fission, a type of asexual reproduction. (ii) In stage P, inside the protective cyst, the nucleus divides repeatedly to form many nuclei; the cytoplasm then divides so that a small part of it surrounds each nucleus, forming many small daughter cells within the cyst. When conditions become favourable the cyst breaks and the daughter cells are released. (iii) Plasmodium (the malarial parasite). (iv) Vegetative propagation, for example by layering, grafting or cuttings (as for banana, orange, rose and jasmine). Advantages: the plants bear flowers and fruits earlier than plants grown from seeds; all the plants are genetically similar to the parent, so its desirable characters are kept.
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark

    Also in 31/3/1 (Q19), 31/3/2 (Q21)

    In the following equation and respectively are :
    1. (a)2, 2
    2. (b)1, 2
    3. (c)2, 1
    4. (d)1, 1
    Show answer
    (a) 2, 2
    Step-by-step solution →
  2. Q18 1 mark

    Also in 31/3/1 (Q17), 31/3/2 (Q23)

    Which of the following is an example of a displacement reaction ?
    1. (a)The combustion of natural gas
    2. (b)The reaction of a reactive metal with dilute acid
    3. (c)The electrolysis of water
    4. (d)The reaction of quick lime with water
    Show answer
    (b) The reaction of a reactive metal with dilute acid
    Step-by-step solution →
  3. Q19 1 mark

    Also in 31/3/1 (Q18), 31/3/2 (Q22)

    To a small amount of copper oxide in a beaker, when we add dilute hydrochloric acid slowly with stirring, the change in the colour of the solution is due to the formation of :
    1. (a)Copper(II) oxide, which is black in colour.
    2. (b)Copper(I) chloride, which is blue in colour.
    3. (c)Copper(II) chloride, which is blue-green in colour.
    4. (d)Copper(I) oxide, which is black in colour.
    Show answer
    (c) Copper(II) chloride, which is blue-green in colour.
    Step-by-step solution →
  4. Q20 1 mark
    Which of the following compounds does not undergo addition reaction ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  5. Q21 1 mark

    Also in 31/3/1 (Q23), 31/3/2 (Q17)

    When zinc reacts with , the product formed is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (c)
    Step-by-step solution →
  6. Q22 1 mark

    Also in 31/3/1 (Q21), 31/3/2 (Q19)

    The reaction of calcium with cold water is :
    1. (a)Less violent, but the heat evolved is sufficient for the hydrogen to catch fire.
    2. (b)Very violent and exothermic and hydrogen catches fire.
    3. (c)Exothermic, but the heat evolved is not sufficient for the hydrogen to catch fire.
    4. (d)Slow and endothermic.
    Show answer
    (c) Exothermic, but the heat evolved is not sufficient for the hydrogen to catch fire.
    Step-by-step solution →
  7. Q23 1 mark

    Also in 31/3/1 (Q22), 31/3/2 (Q18)

    In which case/cases will the bulb glow considering that all other connections of electric circuit are complete and working ?
    + − (i) + − (ii) + − (iii) Battery Bulb Switch Beaker Iron nails Glucose solution Rubber cork Alcohol solution Dilute HCl
    1. (a)Case (i) only
    2. (b)Case (ii) only
    3. (c)Cases (ii) and (iii)
    4. (d)Case (iii) only
    Show answer
    (d) Case (iii) only
    Step-by-step solution →
  8. Q24 1 mark

    Also in 31/3/1 (Q24), 31/3/2 (Q24)

    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): There are large number of compounds with many carbon atoms linked to each other.

    Reason (R): Carbon-Carbon bond is very strong and stable.

    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 →

Question 25 · 2 marks

  1. Q25 2 marks
    Show the formation of NaCl by transfer of electrons. Why does solid NaCl not conduct electricity ? [Atomic number : , ]
    Show answer

    Sodium gives one electron to chlorine to form ; solid NaCl does not conduct because its ions are fixed and cannot move.

    Formation: sodium, , loses its one valence electron to chlorine, , so that and . The ions and both have complete outer shells and are held together by strong electrostatic attraction, giving . Solid sodium chloride does not conduct electricity because its ions are held in fixed positions in the crystal by strong forces of attraction and are not free to move; it conducts only when molten or dissolved in water, when the ions can move to the electrodes.
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26 3 marks
    Define the following terms :
    1. (i)Corrosion
    2. (ii)Rancidity
    3. (iii)Exothermic reaction
    Show answer

    Corrosion is attack on a metal by moisture, air or acids; rancidity is oxidation of fats and oils; an exothermic reaction releases heat.

    (i) Corrosion: when a metal is attacked by the substances around it, such as moisture, air and acids, it is said to corrode, and this process is called corrosion; the rusting of iron is the commonest example. (ii) Rancidity: when fats and oils are oxidised, they become rancid and their smell and taste change; this change is called rancidity. (iii) Exothermic reaction: a reaction in which heat is released along with the formation of the products, for example .
    Step-by-step solution →
  2. Q27(a) 3 marks

    Also in 31/3/1 (Q27(a)), 31/3/2 (Q27(a))

    Give reasons :
    1. (i)For dilution of an acid, acid is added into water and not water into acid.
    2. (ii)Dry gas does not turn blue litmus red whereas dilute hydrochloric acid does.
    3. (iii)Blue colour of Copper(II) sulphate crystals turns white on heating.
    Show answer

    Mixing acid with water is highly exothermic; ions form only in water; heating removes the water of crystallisation that makes copper sulphate blue.

    (i) Dissolving an acid in water is highly exothermic. If water is added to a concentrated acid, the small amount of water is heated so much that the mixture can splash out and cause burns, and the container may crack from local overheating; adding the acid slowly to a large amount of water, with stirring, lets the water absorb the heat safely. (ii) Hydrogen ions, which turn blue litmus red, are produced only in the presence of water: . Dry gas contains no ions, but dilute hydrochloric acid does. (iii) The blue colour is due to the water of crystallisation in . On heating this water is lost and white anhydrous copper sulphate remains: .
    Step-by-step solution →
    OR
    Q27(b) 3 marks

    Also in 31/3/1 (Q27(b)), 31/3/2 (Q27(b))

    Write the preparation of the following compounds with balanced chemical equation :
    1. (i) by chlor-alkali process
    2. (ii)Baking Soda
    3. (iii)Plaster of Paris
    Show answer

    Electrolysis of brine gives sodium hydroxide; brine with ammonia and carbon dioxide gives baking soda; heating gypsum at 373 K gives Plaster of Paris.

    (i) Electricity is passed through brine (aqueous sodium chloride); chlorine forms at the anode, hydrogen at the cathode and sodium hydroxide solution near the cathode: . (ii) Ammonia and carbon dioxide are passed through brine, and sodium hydrogencarbonate (baking soda) separates out: . (iii) Gypsum is heated at K and loses part of its water of crystallisation: (Plaster of Paris) .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks

    Also in 31/3/1 (Q28), 31/3/2 (Q28)

    Read the following passage and answer the questions that follow : An electrochemical process is used for refining metals by selectively dissolving and depositing them through electrolysis. Electrolytic refining is used for metals like Copper, Zinc, Tin, Nickel, Silver and Gold.
    1. (a)Define anode mud.[1]
    2. (b)In electrolytic refining of copper, name the anode and the cathode.[1]
    3. (c)(i)With the help of chemical equations, show the extraction of copper from its ore .[2]
    4. (c)(ii)OR : Draw a neat and labelled diagram showing electrolytic refining of copper.[2]
    Show answer

    Anode mud settles below the anode; the anode is impure copper and the cathode pure copper; heating copper sulphide in air gives copper.

    (a) Anode mud is the deposit of insoluble impurities that settles at the bottom of the tank, below the anode, during electrolytic refining; it contains less reactive metals such as silver and gold. (b) Anode: a thick block of impure copper (joined to the positive terminal). Cathode: a thin strip of pure copper (joined to the negative terminal). The electrolyte is acidified copper sulphate solution. (c)(i) is heated in air: ; the copper(I) oxide then reacts with the remaining sulphide (self-reduction): . OR (c)(ii) A tank of acidified copper sulphate solution; the impure copper anode joined to the positive terminal of a battery and the thin pure copper cathode joined to the negative terminal; ions moving from the anode to the cathode; anode mud collecting below the anode (see the labelled figure).
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks

    Also in 31/3/1 (Q29(a)), 31/3/2 (Q29(a))

    1. (i)What is homologous series ? Which two of the following organic compounds belong to the same homologous series ? , , ,
    2. (ii)Write the product(s) in the following reactions : (I) (II)
    3. (iii)Why does micelle formation take place when soap is added to water ?
    Show answer

    and are in one series; products are ethyl ethanoate with water, and carbon dioxide with water; soap tails cluster inward, forming micelles.

    (i) A homologous series is a series of carbon compounds having the same functional group and the same general formula, in which successive members differ by a unit ( u); they have similar chemical properties and a gradation in physical properties. and belong to the same series (alkenes, ). (ii) (I) Ethyl ethanoate and water: . (II) Carbon dioxide and water, with heat and light: . (iii) A soap molecule has an ionic (hydrophilic) end that interacts with water and a long hydrocarbon (hydrophobic) tail that is repelled by water but interacts with oil and dirt. In water the tails cluster together inside, around any oily dirt, while the ionic ends stay outside facing the water, so the soap molecules form spherical clusters called micelles.
    Step-by-step solution →
    OR
    Q29(b) 5 marks

    Also in 31/3/1 (Q29(b)), 31/3/2 (Q29(b))

    1. (i)Name the following compounds : (I) (II)
    2. (ii)Name the reaction which is commonly used in the conversion of vegetable oils to fats.
    3. (iii)Why is the melting point of higher than ?
    4. (iv)What happens when a piece of sodium is dropped into ethanol ?
    5. (v)Write the products in the following reaction :
    Show answer

    Propanone and propyne; hydrogenation; has the higher molecular mass; sodium gives hydrogen and sodium ethoxide; the ester gives sodium ethanoate and ethanol.

    (i) (I) Propanone (acetone); (II) Propyne. (ii) Hydrogenation: hydrogen is added to the vegetable oil in the presence of a nickel (or palladium) catalyst. (iii) has one more unit and a higher molecular mass ( u) than ( u); in a homologous series melting points rise with molecular mass, as the larger molecules attract one another more strongly. (iv) Sodium reacts with ethanol, giving off bubbles of hydrogen gas and forming sodium ethoxide: . (v) Sodium ethanoate and ethanol: (saponification).
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark

    Also in 31/3/1 (Q30)

    The correct way to connect an ammeter and a voltmeter in an electric circuit is :
    1. (a)Ammeter in parallel and voltmeter in series
    2. (b)Ammeter and voltmeter both in parallel
    3. (c)Ammeter in series and voltmeter in parallel
    4. (d)Ammeter and voltmeter both in series
    Show answer
    (c) Ammeter in series and voltmeter in parallel
    Step-by-step solution →
  2. Q31 1 mark
    Vision defect far-sightedness is found in the eye defects named as :
    1. (a)Myopia and cataract
    2. (b)Myopia and hypermetropia
    3. (c)Presbyopia and hypermetropia
    4. (d)Presbyopia and myopia
    Show answer
    (c) Presbyopia and hypermetropia
    Step-by-step solution →
  3. Q32 1 mark

    Also in 31/3/1 (Q32), 31/3/2 (Q32)

    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): The needle of a compass, kept in an external magnetic field, always aligns itself in the North-South direction of the Earth.

    Reason (R): The behaviour of the needle of the compass is similar to the behaviour of a freely suspended bar magnet.

    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.
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Questions 33–34 · 2 marks each

  1. Q33 2 marks
    Draw the ray diagram showing refraction through a glass slab and write the relation between angle of incidence, angle of refraction and refractive index of glass.
    Show answer

    The ray bends towards the normal on entering and away on leaving, emerging parallel; .

    Ray diagram: see the figure. The incident ray bends towards the normal on entering the glass (angle of refraction less than ), and bends away from the normal on leaving it at , emerging along at an angle of emergence - parallel to the incident ray but laterally displaced. Relation (Snell's law): , where is the angle of incidence in air, the angle of refraction in glass and the refractive index of glass with respect to air.
    Step-by-step solution →
  2. Q34(a) 2 marks

    Also in 31/3/1 (Q34(a)), 31/3/2 (Q33(a))

    What happens when light is scattered from
    1. (i)very fine particles and
    2. (ii)very large size particles of medium ? Justify your answer in each case.
    Show answer

    Very fine particles scatter mainly blue light; very large particles scatter all wavelengths almost equally, so the light appears white.

    (i) Very fine particles (much smaller than the wavelength of light, such as air molecules) scatter the shorter wavelengths far more than the longer ones, so mainly blue light is scattered and the scattered light appears blue - the reason the clear sky is blue. Justification: red light has a wavelength about times that of blue, and fine particles scatter short wavelengths much more strongly. (ii) Very large particles (larger than the wavelength, such as the water droplets of clouds) scatter all wavelengths nearly equally, so the scattered light contains all the colours and appears white - the reason clouds look white. Justification: no colour is favoured, and a mixture of all colours in their original proportions is white.
    Step-by-step solution →
    OR
    Q34(b) 2 marks

    Also in 31/3/1 (Q34(b)), 31/3/2 (Q33(b)), 31/8/1/SB (Q33(b)), 31/8/2/SB (Q34(b)), 31/8/3/SB (Q34(b))

    With the help of a ray diagram, explain any phenomenon of formation of spectrum in nature.
    Show answer

    A rainbow forms when raindrops disperse sunlight by refraction, internal reflection and refraction, giving a spectrum with red outside and violet inside.

    The rainbow is a natural spectrum formed after rain by the dispersion of sunlight by tiny water droplets in the atmosphere. Each droplet acts like a small prism: sunlight is refracted and dispersed as it enters the drop, reflected internally at the back surface, and refracted again as it comes out (see the ray diagram). The colours emerge at slightly different angles - red at about , violet at about to the direction opposite the Sun - so an observer standing with the Sun behind sees a band of colours in the sky, red on the outside and violet on the inside, always on the side opposite the Sun.
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks

    Also in 31/3/1 (Q37), 31/3/2 (Q36)

    Consider the given electric circuit : Calculate the following :
    1. (a)Total resistance of the circuit
    2. (b)The electric current drawn from the battery
    3. (c)Potential difference between points P and Q
    A + − 10 V 1 Ω 4 Ω 5 Ω 5 Ω 3 Ω 2 Ω S R Q P + −
    Show answer

    Total resistance is , the battery supplies A, and the potential difference between P and Q is V.

    (a) Total resistance : between S and R, in parallel with gives ; between Q and P, in parallel with gives ; in series, . (b) Current drawn from the battery A. (c) Potential difference between P and Q V.
    Step-by-step solution →
  2. Q36 3 marks

    Also in 31/3/1 (Q35), 31/3/2 (Q37)

    Study the given diagram and answer the questions that follow :
    1. (a)Write the name of the eye defect shown in the diagram. Where is the image formed in this eye defect with respect to the retina of the eye ?
    2. (b)List two causes of this eye defect.
    3. (c)With the help of a diagram, show how this eye defect of vision is corrected.
    N N′
    Show answer

    The defect is hypermetropia: the image forms behind the retina; a convex lens corrects it.

    (a) The defect is hypermetropia (far-sightedness). The image of a nearby object is formed behind the retina. (b) Two causes: the focal length of the eye lens is too long (the eye lens is not converging enough), and the eyeball has become too small. (c) It is corrected with spectacles having a convex (converging) lens of suitable power: the lens makes the rays from a nearby object at less divergent, so that they appear to come from the farther point , the near point of this eye, and the eye lens then focuses them on the retina (see the diagram).
    Step-by-step solution →
  3. Q37 3 marks
    1. (a)State Ohm's law and justify that V – I graph for Ohm's law will always be a straight line passing through the origin.
    2. (b)The figure shows V – I graphs for two identical wires A and B having the same length and area of cross-section, but made of different materials. Which of these wires will be more suitable for making the heating element of an electric heater and why ?
    B A Potential difference (V) Electric Current (I)
    Show answer

    At constant temperature , so the graph is a straight line through the origin; wire B is better for heating.

    (a) Ohm's law: the potential difference across the ends of a given metallic wire is directly proportional to the current flowing through it, provided its temperature remains the same; that is, , where the resistance is a constant. Justification: with constant, has the form , which is a straight line of constant slope , and when , so the line passes through the origin. (b) Wire B. Its - graph is the steeper one, so for the same current it needs a larger potential difference and its resistance is larger. Since both wires have the same length and the same area of cross-section, shows that B's material has the higher resistivity; a heating element is made of a high-resistivity material, which produces more heat () for the current it carries.
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks

    Also in 31/3/1 (Q38), 31/3/2 (Q38)

    The variation of image distance () with the object distance () for a convex lens is given in the following observation table. Analyse it and answer the questions given below :
    S.No.Object distance () cmImage distance () cm
    1
    2
    3
    4
    5
    6
    1. (a)Without calculation, find out the focal length of the given convex lens. Justify your answer.[1]
    2. (b)Which one of the observations given in the table is not correct and why ?[1]
    3. (c)(i)Find out the value of magnification for cm. Write the nature of the image formed. Give reason for your answer.[2]
    4. (c)(ii)OR : Analyse the data given in the table above and draw the labelled ray diagram for cm and cm.[2]
    Show answer

    cm; observation 6 is incorrect because must be negative; , so the image is real, inverted and magnified.

    (a) cm. In observation 3 the object is at cm and the image at cm, the same distance on the other side of the lens, which happens only when the object stands at ; hence cm and cm. (b) Observation 6 ( cm, cm) is not correct. The object is only cm from the lens, inside its focal length of cm, and a convex lens then forms a virtual, erect, magnified image on the same side as the object, so must be negative - the lens formula gives cm, not cm. (c)(i) . The image is real, inverted and magnified, five times the size of the object, because is negative (inverted, and so real) and (enlarged); the object at cm lies between and , which is the position that gives such an image beyond . OR (c)(ii) With cm, the object stands at cm, between and . The ray from parallel to the axis passes through after refraction and the ray from through goes on undeviated; they meet at , cm behind the lens and beyond , giving a real, inverted image five times the height of the object (see the ray diagram).
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    A person was repairing an electric heater. He observed that there were three different connecting wires of three different colours in the cable attached to the heater.
    1. (i)What are these three different wires called ? Name them colourwise.
    2. (ii)What is the value of standard potential difference at which electricity is supplied in Indian homes for lighting ?
    3. (iii)What is the role of (I) earthing and (II) fuse in domestic electric circuits ?
    Show answer

    The wires are live (red), neutral (black) and earth (green); supply is 220 V; earthing prevents shock and a fuse stops excess current.

    (i) The three wires are the live wire (positive), with red insulation; the neutral wire (negative), with black insulation; and the earth wire, with green insulation. (ii) V (alternating current, of frequency Hz). (iii) (I) Earthing: the earth wire joins the metallic body of the appliance to a metal plate buried deep in the earth. If the live wire touches the body, the leakage current flows to the earth through this low-resistance path, the body stays at the potential of the earth, and the user does not receive a severe electric shock. (II) Fuse: a short wire of low melting point, connected in series with the live wire. When the current exceeds the safe value because of overloading or short-circuiting, the heat produced melts the fuse wire and breaks the circuit, protecting the appliances and the wiring from damage and fire.
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)Write the name and statement of the rule used to determine the direction of the : (I) force experienced by a straight current-carrying conductor placed in a uniform magnetic field perpendicular to the field. (II) magnetic field produced around a straight conductor carrying electric current.
    2. (ii)Two straight current-carrying conductors (A) and (B) are shown in the figures below : (I) Mark the direction of the magnetic fields around these current-carrying conductors (A) and (B). (II) Compare the strengths of magnetic fields produced (1) at points P and Q and (2) at points Q and R due to these current-carrying conductors, qualitatively.
    I = 1 A O P 2 cm I = 2 A O Q 2 cm 4 cm R (A) (B)
    Show answer

    Fleming's left-hand rule; right-hand thumb rule; the field is anticlockwise round A, clockwise round B, and stronger at Q than at P or R.

    (i) (I) Fleming's left-hand rule: stretch the thumb, the forefinger and the middle finger of the left hand so that they are mutually perpendicular; if the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, the thumb points in the direction of the force (the motion) on the conductor. (II) Right-hand thumb rule: imagine holding the current-carrying straight conductor in the right hand with the thumb pointing in the direction of the current; the fingers then wrap around the conductor in the direction of the magnetic field lines. (ii) (I) Around (A), where the current flows upwards, the field lines are anticlockwise circles as seen from above; around (B), where the current flows downwards, they are clockwise circles as seen from above - see the marked figure. (II) (1) The field at Q is stronger than the field at P: both points are cm from their conductors, but (B) carries the larger current ( A against A). (2) The field at Q is stronger than the field at R: both are due to the same current of A, but Q is nearer the conductor ( cm against cm).
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