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CBSE Class 10 Science 2026 — Paper 31/1/1

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

35 of its 45 questions also appear in 31/1/3 or 31/1/2; 10 are only in this paper.

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Questions 1–9 · 1 mark each

  1. Q1 1 mark

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

    Which structure in a leaf is mainly responsible for gaseous exchange ?
    1. (a)Xylem
    2. (b)Stomata
    3. (c)Phloem
    4. (d)Cuticle
    Show answer
    (b) Stomata
    Step-by-step solution →
  2. Q2 1 mark
    Identify the type of reproduction shown in the diagram given below :
    1. (a)Budding
    2. (b)Fragmentation
    3. (c)Spore Formation
    4. (d)Binary Fission
    Show answer
    (d) Binary Fission
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/1/2 (Q6), 31/1/3 (Q1)

    Identify the correct statement for spirogyra, leishmania and hydra :
    1. (a)they reproduce sexually.
    2. (b)they are unicellular.
    3. (c)they are multicellular.
    4. (d)they reproduce asexually.
    Show answer
    (d) they reproduce asexually.
    Step-by-step solution →
  4. Q4 1 mark

    Also in 31/1/2 (Q5)

    Human brain has various parts or regions that help in different actions, responses and coordination. From the following, identify the part responsible for precision of voluntary actions :
    1. (a)Cerebrum
    2. (b)Cerebellum
    3. (c)Medulla
    4. (d)Pons
    Show answer
    (b) Cerebellum
    Step-by-step solution →
  5. Q5 1 mark

    Also in 31/1/2 (Q7), 31/1/3 (Q3)

    Pancreas secretes pancreatic juice which contain certain enzyme that helps in digestion of food. Choose the correct option from the following :
    1. (a)Trypsin digests emulsified fats and lipase digests proteins.
    2. (b)Trypsin digests proteins and lipase digests emulsified fats.
    3. (c)Trypsin and lipase both digests fats.
    4. (d)Trypsin digests proteins and lipase digests carbohydrates.
    Show answer
    (b) Trypsin digests proteins and lipase digests emulsified fats.
    Step-by-step solution →
  6. Q6 1 mark
    Sex is determined by different factors in various species. However, in human beings, it is determined genetically. Which amongst the following option(s) is/are correct for human beings ?
    1. (i)Gamete carrying X chromosome from female parent.
    2. (ii)Gamete carrying X chromosome from male parent.
    3. (iii)Gamete carrying Y chromosome from male parent.
    1. (a)(ii) and (iii)
    2. (b)(i) only
    3. (c)(i) and (iii)
    4. (d)(iii) only
    Show answer
    (a) (ii) and (iii)
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/1/2 (Q4), 31/1/3 (Q5)

    Which of the following group is not ‘biodegradable’ ?
    1. (a)Vegetable peels, dead leaves, paper
    2. (b)Cow dung, leather bag, water
    3. (c)Polythene bag, rubber band, ball pen
    4. (d)Paper, fruits, bones
    Show answer
    (c) Polythene bag, rubber band, ball pen
    Step-by-step solution →
  8. Q8 1 mark

    Also in 31/1/3 (Q8)

    Directions : Question numbers 8 and 9 are Assertion and Reason based questions. Two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :

    Assertion (A): Reflex actions do not involve thinking.

    Reason (R): Most reflex actions are controlled by the spinal cord.

    1. (a)Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 the Assertion (A).
    Step-by-step solution →
  9. Q9 1 mark

    Also in 31/1/2 (Q8)

    Directions : Question numbers 8 and 9 are Assertion and Reason based questions. Two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :

    Assertion (A): In human beings, the respiratory pigment is haemoglobin present in red blood cells.

    Reason (R): Haemoglobin has a very high affinity for carbon dioxide.

    1. (a)Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 →

Questions 10–12 · 2 marks each

  1. Q10 2 marks
    What is the function of diaphragm in human respiratory system ? Where is it present in human body ?
    Show answer

    The diaphragm is a muscular sheet below the lungs that changes the chest volume to draw air in and push it out.

    Position: The diaphragm is a dome-shaped sheet of muscle just below the lungs. It forms the floor of the chest (thoracic) cavity and separates it from the abdominal cavity. Function: It brings about breathing by changing the volume of the chest cavity. When it contracts and flattens, with the ribs lifted, the chest cavity enlarges, the pressure in the lungs falls and air is drawn in; when it relaxes and returns to its dome shape, the chest cavity becomes smaller and air is pushed out.
    Step-by-step solution →
  2. Q11(a) 2 marks

    Also in 31/1/2 (Q10(a)), 31/1/3 (Q12(a))

    State two differences between the act of chewing food and salivation on sight of food.
    Show answer

    Chewing is voluntary and controlled by the fore-brain; salivation on sight of food is involuntary and controlled by the medulla.

    1. Chewing food is a voluntary action: we decide to chew and can start or stop it at will. Salivation on sight of food is an involuntary action: the mouth waters automatically and we cannot stop it by thinking. 2. Chewing is controlled by the fore-brain (cerebrum) and is carried out by the muscles of the jaw. Salivation is controlled by the medulla in the hind-brain and is carried out by the salivary glands.
    Step-by-step solution →
    OR
    Q11(b) 2 marks

    Also in 31/1/2 (Q10(b)), 31/1/3 (Q12(b))

    State two differences between pollination and fertilization.
    Show answer

    Pollination transfers pollen to the stigma, whereas fertilisation fuses the male and female germ cells; pollination occurs only in plants.

    1. Pollination is the transfer of pollen grains from the anther to the stigma of a flower, whereas fertilisation is the fusion of the male germ cell with the female germ cell (egg) to form a zygote. 2. Pollination occurs only in plants, whereas fertilisation occurs in both plants and animals. Another acceptable difference: pollination takes place on the stigma, outside the ovary, and transfer between flowers needs agents such as wind, water or insects, whereas fertilisation takes place inside the ovule, after the pollen tube has carried the male germ cell there, and needs no outside agent.
    Step-by-step solution →
  3. Q12 2 marks

    Also in 31/1/3 (Q11)

    Draw a neat diagram to show germination of pollen on the female reproductive part of the flower. Name and label only the following parts :
    1. (a)The part that receives the pollen grain.
    2. (b)The structure that carries the male germ cell to reach the female germ cell.
    Show answer

    The stigma receives the pollen grain, and the pollen tube carries the male germ cell down to the female germ cell in the ovule.

    (a) Stigma: the sticky top of the pistil, which receives the pollen grain. (b) Pollen tube: it grows out of the germinating pollen grain, down through the style, to the ovule, and carries the male germ cell to the female germ cell. The diagram shows the pistil (stigma, style and ovary with an ovule) with pollen grains on the stigma and a pollen tube growing from one of them down to the ovule; only Stigma and Pollen tube are labelled.
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks

    Also in 31/1/2 (Q14), 31/1/3 (Q14)

    Given below is a pyramid showing various trophic levels in an ecosystem :
    1. (a)From the organisms listed below, identify which one is to be placed at which trophic level ? Deer, Grass, Lion, Snake, Rabbit
    2. (b)Discuss the reason why primary consumers will have more energy as compared to secondary consumers ?
    3. (c)Why is the base of the pyramid broad ?
    (iv) (iii) (ii) (i) Tertiary consumers Secondary consumers Primary consumers Producers
    Show answer

    Grass is the producer, deer and rabbit are primary consumers, snake secondary, lion tertiary; each level passes on only about 10% of its energy.

    (a) (i) Producers: Grass; (ii) Primary consumers: Deer and Rabbit; (iii) Secondary consumers: Snake (the lion also feeds at this level when it eats deer); (iv) Tertiary consumers: Lion. (b) At each trophic level most of the food energy is used up in life processes and lost as heat; only about is passed on to the next level. Primary consumers get energy directly from producers, whereas secondary consumers get only about of the energy of the primary consumers, so primary consumers have more energy. (c) The base is formed by the producers, which trap solar energy directly and so hold the maximum energy (and, in a grassland, the largest number of organisms); because only about of the energy passes to each higher level, every level above receives less energy and supports less life, so the base is the broadest.
    Step-by-step solution →
  2. Q14 3 marks

    Also in 31/1/3 (Q13)

    Give differences between the following :
    1. (a)Nephron and neuron
    2. (b)Sensory nerve and motor nerve
    3. (c)Consumers and decomposers
    Show answer

    Nephron forms urine, neuron conducts impulses; sensory nerves carry impulses to the CNS, motor nerves from it; consumers eat, decomposers break down dead remains.

    (a) Nephron: the structural and functional unit of the kidney; it filters the blood and forms urine. Neuron: the structural and functional unit of the nervous system; it receives and conducts information as electrical impulses. (b) Sensory nerve: carries impulses from the receptors of the sense organs to the brain or spinal cord. Motor nerve: carries impulses from the brain or spinal cord to the effectors, that is, muscles and glands. (c) Consumers: get their food directly or indirectly from the producers by eating plants or other animals, and pass food energy along the food chain. Decomposers: micro-organisms such as bacteria and fungi that feed on dead remains and wastes, breaking them down into simple substances that return to the soil.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks

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

    Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the generation. Answer the following questions :
    1. (a)Why only tall pea plants were observed in progeny ?[1]
    2. (b)By which method did Mendel obtain progeny ?[1]
    3. (c)(i)Write one difference between dominant and recessive trait.[2]
    4. (c)(ii)OR : Write two observations made by Mendel about progeny.[2]
    Show answer

    Tallness is dominant, so all are and tall; self-pollination gives in the ratio ; a recessive trait needs two factors.

    (a) Tallness is dominant over shortness. Every plant received from the tall parent and from the short parent, so all were ; in the dominant is expressed and is masked, so all were tall. (b) By self-pollination of the tall plants (), which gave tall and short plants in the ratio in the . (c)(i) A dominant trait is expressed even when only one factor for it is present (), so it appears in the ; a recessive trait is expressed only when both factors are recessive (), so it is hidden in the and reappears in the . OR (c)(ii) All the plants were tall, showing the trait of only one parent; and none was short or of medium height, so the parental traits did not blend.
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks

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

    Given below are certain situations. Analyse each and describe its possible impact :
    1. (i)A population of bacteria living in temperate waters whose temperature increased by global warming.
    2. (ii)The sperm encounters the egg when it reaches the oviduct in human females.
    3. (iii)Self pollination does not occur in a flower that contains only pistil.
    4. (iv)Egg does not get fertilised in a human female.
    5. (v)When the seed is placed under appropriate condition of water and air in the soil ?
    Show answer

    Heat-resistant bacteria survive, fertilisation leads to pregnancy, a pistil-only flower needs cross-pollination, an unfertilised egg causes menstruation, and a seed germinates.

    (i) Most of the bacteria would die in the warmer water, but a few variants that are resistant to heat would survive and multiply, so the species survives; this shows the importance of variation. (ii) Fertilisation occurs in the oviduct and a zygote is formed; it divides, gets implanted in the thick lining of the uterus and develops into an embryo, nourished through the placenta, so the woman becomes pregnant. (iii) The flower is unisexual (female) and has no pollen of its own, so it can be pollinated only by cross-pollination, with pollen brought from another flower by wind, water or animals; without that pollen no seeds or fruit form. (iv) The egg lives for about a day; the thick, blood-rich lining of the uterus is not needed, so it breaks down and comes out through the vagina as blood and mucus: menstruation, lasting about two to eight days. (v) The seed germinates: the embryo grows using food stored in the cotyledons, the radicle forms the root and the plumule the shoot, and a seedling develops.
    Step-by-step solution →
    OR
    Q16(b) 5 marks

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

    Given below are certain situations. Analyse and describe what would happen when :
    1. (i)Spores are liberated from blob-like structures of the bread mould?
    2. (ii)Leaves of bryophyllum fall on wet soil ?
    3. (iii)A pollen from different species land on the stigma of totally unrelated species ?
    4. (iv)Copper-T is placed in the uterus of a human female ?
    5. (v)Spirogyra breaks into smaller fragments upon maturation ?
    Show answer

    Spores, Bryophyllum buds and Spirogyra fragments each grow into new individuals; unrelated pollen fails to fertilise, and Copper-T prevents pregnancy.

    (i) The blob-like structures are sporangia; the spores released from them are carried by air, and on reaching a moist surface such as bread each spore germinates into a new bread mould (spore formation). (ii) Buds in the notches along the leaf margin develop roots and shoots and grow into new Bryophyllum plants (vegetative propagation). (iii) The pollen does not germinate, or its pollen tube does not grow down to the ovule, on the stigma of an unrelated species, so fertilisation does not occur and no seed forms. (iv) The copper-T, a contraceptive device, prevents pregnancy; it may cause side effects due to irritation of the uterus. (v) Each fragment grows into a new Spirogyra filament, a new individual (fragmentation).
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark

    Also in 31/1/2 (Q23), 31/1/3 (Q18)

    1. (i)
    2. (ii) Which of the following options clearly describes both the reactions ?
    1. (a)(i) is double displacement, (ii) is displacement reaction.
    2. (b)Both, (i) and (ii) are displacement reactions and precipitation reactions.
    3. (c)Both, (i) and (ii) are double displacement reactions and precipitation reactions.
    4. (d)(i) is displacement, (ii) is double displacement reaction.
    Show answer
    (c) Both, (i) and (ii) are double displacement reactions and precipitation reactions.
    Step-by-step solution →
  2. Q18 1 mark

    Also in 31/1/2 (Q22), 31/1/3 (Q19)

    Which one of the following can be used as an acid-base indicator by a visually impaired (blind) student ?
    1. (a)Turmeric
    2. (b)Vanilla essence
    3. (c)Methyl orange
    4. (d)Litmus
    Show answer
    (b) Vanilla essence
    Step-by-step solution →
  3. Q19 1 mark

    Also in 31/1/2 (Q21), 31/1/3 (Q17)

    The gases evolved on heating lead (II) nitrate crystals are :
    1. (a) and
    2. (b) and
    3. (c) and
    4. (d) and
    Show answer
    (d) and
    Step-by-step solution →
  4. Q20 1 mark
    The formula of functional group for aldehyde is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (b)
    Step-by-step solution →
  5. Q21 1 mark

    Also in 31/1/2 (Q19), 31/1/3 (Q22)

    Which of the following is a poor conductor of electricity ?
    1. (a)Pb
    2. (b)Cu
    3. (c)Ag
    4. (d)Al
    Show answer
    (a) Pb
    Step-by-step solution →
  6. Q22 1 mark

    Also in 31/1/2 (Q18), 31/1/3 (Q23)

    The natural sources of oxalic acid, lactic acid and methanoic acid respectively are :
    1. (a)tomato, curd, ant-sting
    2. (b)tomato, orange, nettle-sting
    3. (c)orange, milk, ant-sting
    4. (d)orange, sour milk, nettle-sting
    Show answer
    (a) tomato, curd, ant-sting
    Step-by-step solution →
  7. Q23 1 mark

    Also in 31/1/2 (Q17), 31/1/3 (Q21)

    When an element ‘X’ reacts with water, it starts floating. Identify the element ‘X’ :
    1. (a)Potassium
    2. (b)Calcium
    3. (c)Sodium
    4. (d)Iron
    Show answer
    (b) Calcium
    Step-by-step solution →
  8. Q24 1 mark

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

    Directions : For question number 24, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below :

    Assertion (A): Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements.

    Reason (R): The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.

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

Question 25 · 2 marks

  1. Q25 2 marks
    1. (a)What are amphoteric oxides ?
    2. (b)Categorise the following based on their nature : , ,
    Show answer

    Amphoteric oxides react with both acids and bases; is amphoteric, basic and acidic.

    (a) Amphoteric oxides are metal oxides that react with both acids and bases to produce a salt and water, for example and . (b) is an amphoteric oxide, is a basic oxide and is an acidic oxide.
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26 3 marks
    1. (a)Name the substance oxidised and reduced in the following reaction :
    2. (b)Balance the following chemical reaction :
    3. (c)Give one example each of electrolytic decomposition and decomposition by sunlight.
    Show answer

    Carbon is oxidised, zinc oxide reduced; the equation needs and ; examples are electrolysis of water and silver chloride in sunlight.

    (a) Carbon () is oxidised to , and zinc oxide () is reduced to . (b) (c) Electrolytic decomposition: ; decomposition by sunlight: .
    Step-by-step solution →
  2. Q27(a) 3 marks

    Also in 31/1/2 (Q26(a)), 31/1/3 (Q27(a))

    Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.
    Show answer

    Brine electrolysis gives chlorine at the anode, hydrogen at the cathode and sodium hydroxide near the cathode.

    The chlor-alkali process is the electrolysis of brine, a concentrated aqueous solution of sodium chloride. The electric current decomposes it into sodium hydroxide, chlorine and hydrogen; the name comes from chlorine ("chlor") and sodium hydroxide ("alkali"). Anode: chlorine gas, . Cathode: hydrogen gas, ; sodium hydroxide solution is formed near the cathode.
    Step-by-step solution →
    OR
    Q27(b) 3 marks

    Also in 31/1/2 (Q26(b)), 31/1/3 (Q27(b))

    Write the preparation of following compounds with balanced chemical equation :
    1. (i)Baking soda
    2. (ii)Bleaching powder
    3. (iii)Plaster of Paris
    Show answer

    Baking soda from brine, ammonia and carbon dioxide; bleaching powder from chlorine and dry slaked lime; Plaster of Paris by heating gypsum at 373 K.

    (i) Baking soda () is prepared by passing carbon dioxide and ammonia into brine: . (ii) Bleaching powder () is prepared by the action of chlorine on dry slaked lime: . (iii) Plaster of Paris is prepared by heating gypsum at K: .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks

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

    Read the following passage and answer the questions given below : Most of metals occur in combined state in form of ores. Carbonate ores are converted into oxides by calcination and sulphide ores by roasting. Oxides are reduced with suitable reducing agent like carbon to get free metal. Highly reactive metals like – Al, Mg are also used as reducing agents to obtain metal from their oxides. Most reactive metals are obtained by electrolytic reduction of their molten ores. Alloying is a very good method of improving the properties of a metal. We can get desired properties by this method. The electrical conductivity and melting point of an alloy is less than that of pure metals.
    1. (a)Why carbonate or sulphide ores are converted to oxides before extraction of metal from it ?[1]
    2. (b)Write a reaction in which Aluminium is used as a reducing agent to obtain metal from its oxide.[1]
    3. (c)(i)How is copper obtained from its ore () ? Give equations of the reactions.[2]
    4. (c)(ii)(I)OR : Why highly reactive metals cannot be obtained from their oxides by using carbon as a reducing agent ?[1]
    5. (c)(ii)(II)Why solder, an alloy of lead and tin, is used for welding electrical wires together ?[1]
    Show answer

    Oxides are easier to reduce; aluminium reduces iron oxide; copper sulphide is heated in air; carbon cannot reduce reactive metals; solder melts easily.

    (a) A metal is obtained much more easily from its oxide than from its carbonate or sulphide, because carbon readily reduces the oxide. So carbonate ores are calcined and sulphide ores roasted to the oxide first, e.g. and , followed by . (b) Thermit reaction: . (c)(i) Copper is low in the reactivity series, so is simply heated in air (self-reduction): , then . OR (c)(ii) (I) Highly reactive metals have a greater affinity for oxygen than carbon, so carbon cannot remove oxygen from their oxides; they are obtained by electrolytic reduction of their molten compounds. (II) Solder has a low melting point (lower than that of lead or of tin), so it melts easily and joins the wires without melting them, and the joint still conducts electricity.
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks

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

    1. (i)Give reasons for the following : (I) Covalent compounds are poor conductor of electricity. (II) Soap does not form lather in hard water. (III) Carbon shows catenation but silicon does not.
    2. (ii)Write chemical equations for the following : (I) Oxidation of ethanol by acidified . (II) Hydrogenation of ethene.
    Show answer

    No free ions in covalent compounds; scum forms in hard water; strong C-C bonds give catenation; ethanol gives ethanoic acid, ethene gives ethane.

    (i) (I) In covalent compounds the atoms share electrons, so no ions are formed and there are no free charged particles to carry a current; hence they are poor conductors of electricity. (II) Hard water contains calcium and magnesium salts. Soap reacts with the and ions to form an insoluble precipitate (scum), so the soap is used up and no lather forms. (III) The carbon atom is small, so carbon–carbon bonds are very strong and stable and carbon atoms can join into long chains and rings. Silicon atoms are larger and silicon–silicon bonds are weak, so silicon forms only short, very reactive chains (up to seven or eight atoms). (ii) (I) (ethanol to ethanoic acid). (II) (ethene to ethane).
    Step-by-step solution →
    OR
    Q29(b) 5 marks

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

    Mohan heated ethanol with a compound ‘X’ in the presence of a few drops of conc. and observed a sweet smelling compound ‘Y’ is formed. When ‘Y’ is treated with sodium hydroxide it gives back ethanol and a compound ‘Z’.
    1. (i)Identify ‘X’, ‘Y’ and ‘Z’.
    2. (ii)Write the role of conc. in the reaction.
    3. (iii)Write the chemical equations involved and name the reactions.
    Show answer

    X is ethanoic acid, Y is ethyl ethanoate and Z is sodium ethanoate; concentrated sulphuric acid is a catalyst and a dehydrating agent.

    (i) X is ethanoic acid (acetic acid), ; Y is ethyl ethanoate (ethyl acetate), , a sweet-smelling ester; Z is sodium ethanoate (sodium acetate), . (ii) Concentrated acts as a catalyst for the esterification; as a dehydrating agent it also takes up the water formed. (iii) Esterification: . Saponification: .
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark

    Also in 31/1/2 (Q31), 31/1/3 (Q30)

    A convex lens of focal length cm, is forming a real image. If the size of image is same as the size of object, then position of object and position of image will be, respectively :
    1. (a) cm and cm from lens
    2. (b) cm and cm from lens
    3. (c) cm and cm from lens
    4. (d) cm and cm from lens
    Show answer
    (c) cm and cm from lens
    Step-by-step solution →
  2. Q31 1 mark

    Also in 31/1/2 (Q30), 31/1/3 (Q31)

    When you look at an object very close to your eyes, the :
    1. (a)Ciliary muscles of your eye contract and the eye lens becomes thick.
    2. (b)Ciliary muscles of your eye get relaxed and the eye lens becomes thick.
    3. (c)Ciliary muscles of your eye contract and the eye lens becomes thin.
    4. (d)Ciliary muscles of your eye get relaxed and the eye lens becomes thin.
    Show answer
    (a) Ciliary muscles of your eye contract and the eye lens becomes thick.
    Step-by-step solution →
  3. Q32 1 mark

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

    Directions : For question number 32, two statements are given, one labelled as Assertion (A) and the other is 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 rays of white light pass through a prism, on emerging they give spectrum of seven colours.

    Reason (R): It is due to the scattering of light that red light bends minimum and violet light bends the maximum.

    1. (a)Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 →

Questions 33–34 · 2 marks each

  1. Q33 2 marks
    The given figure shows image formation by a lens. Analyse the figure and answer the following questions :
    1. (a)What is the type of lens used for image formation in the given ray diagram ?
    2. (b)If the real image is formed at a distance of 30 cm from the lens and the size of image is twice the size of the object, then where was the object placed ?
    Lens B′ A′ A B
    Show answer

    The lens is convex (converging); the object was placed 15 cm in front of the lens.

    (a) A convex (converging) lens. The ray parallel to the principal axis is bent towards the axis and crosses it beyond the lens, and the image formed is virtual, erect and enlarged - an image only a convex lens can form, with the object between its optical centre and principal focus. (b) The object was placed cm in front of the lens, on the side opposite to the real image: cm. (The lens then has cm, and the object lies between and .)
    Step-by-step solution →
  2. Q34(a) 2 marks

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

    The resistance of a wire of 0.01 cm radius and 1.0 cm length is 7 Ω. Calculate its resistivity.
    Show answer

    The resistivity of the wire's material is .

    The resistivity of the material of the wire is m (that is, cm).
    Step-by-step solution →
    OR
    Q34(b) 2 marks

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

    An electric heater is rated 220 V; 11 A. Calculate the power consumed if the heater is operated at 200 V.
    Show answer

    W: the heater consumes 2 kW when operated at 200 V.

    The heater consumes W ( kW) at V. Its resistance is , so W.
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks
    A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.
    Show answer

    Hypermetropia, with the near point at 1 m; a convex lens makes rays from 25 cm appear to come from 1 m.

    The person suffers from hypermetropia (far-sightedness): his near point has moved from cm to m, so light from a book held closer than m is focused behind the retina. It is caused by too long a focal length of the eye lens, or by the eyeball becoming too small. It is corrected with spectacles having a convex (converging) lens of suitable power - here cm, D - which makes the rays from a book at cm appear to come from m, so the image forms on the retina. Ray diagrams: (i) The defect - rays from ( m) meet on the retina, while rays from ( cm) would meet behind it; (ii) The correction - the convex lens bends the rays from as if they came from , and the eye focuses them on the retina.
    Step-by-step solution →
  2. Q36 3 marks

    Also in 31/1/2 (Q35), 31/1/3 (Q36)

    1. (a)Describe an activity to show that a current carrying conductor, placed in an external magnetic field experiences a force.
    2. (b)Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally towards the front wall from the back wall, is deflected by a strong magnetic field to your right side. Find the direction of the magnetic field.
    Show answer

    A rod between magnet poles is displaced when current flows, showing a force; the electron-beam field is vertically downwards.

    (a) Suspend a small aluminium rod horizontally from a stand by two connecting wires so that it lies between the poles of a strong horseshoe magnet (north pole below, south pole above), and connect it in series with a battery, a key and a rheostat. When a current is passed, the rod is displaced sideways; when the direction of the current is reversed, or the poles of the magnet are interchanged, it is displaced in the opposite direction. This shows that a current-carrying conductor placed in a magnetic field experiences a force, whose direction depends on the directions of the current and the field (Fleming's left-hand rule). (b) The magnetic field is directed vertically downwards.
    Step-by-step solution →
  3. Q37 3 marks

    Also in 31/1/2 (Q36), 31/1/3 (Q35)

    1. (a)The pattern of magnetic field due to a current carrying wire depends upon the shape made by that wire. Justify.
    2. (b)A current carrying straight wire AB is shown in the given diagram. Out of X, Y and Z on which point will the strength of magnetic field be maximum and why ?
    X Y Z A B Electric Current i
    Show answer

    Wire shape decides the field pattern; the field is maximum at X, the point nearest the wire.

    (a) Each small part of a current-carrying wire produces circular field lines around itself, so the overall field depends on how the wire is laid out. For a straight wire the field lines are concentric circles round the wire; for a circular loop they are small circles near the wire that become nearly straight lines at the centre, at right angles to the plane of the loop; for a solenoid they are parallel straight lines inside (a uniform field) and like those of a bar magnet outside. The same current thus gives different patterns for different shapes. (b) The field is maximum at X, because X is nearest the wire and the magnetic field of a straight current-carrying wire decreases as the distance from the wire increases (its field-line circles are closest together near the wire).
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks

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

    Read the following passage and answer the questions given : Lenses can form different types of images depending upon their focal length and position of object. A convex lens can create real, inverted or virtual, erect images, while a concave lens forms only virtual and diminished images. The focal length determines the power of lens. Convex lenses have positive focal length while concave lenses have negative focal length by convention. When lenses are placed together, their combined power is determined by the sum of their individual powers. Ray diagrams help to visualize how light converges or diverges through lens to form an image.
    1. (a)A convex lens of focal length 20 cm is used to form an image. If an object is placed at 40 cm from the lens, what will be the position and nature of image ?[1]
    2. (b)Illustrate the formation of image with the help of ray diagram, when the object is placed between the optical centre and principal focus of concave lens.[1]
    3. (c) (i)A lens combination consists of a convex lens of focal length 30 cm and a concave lens of focal length 15 cm placed together. Find the equivalent focal length and power of this lens combination.[2]
    4. (c) (ii)OR : Two lenses are placed in contact. One is a concave lens with focal length 2 m and the other is a convex lens with focal length 1.5 m. What type of lens will the combination behave as (convex or concave) ? Give reason.[2]
    Show answer

    Image at cm is real, inverted, same size; a concave lens gives a virtual, diminished image; combination cm, D.

    (a) The image is formed at cm, that is cm on the other side of the lens (at ); it is real, inverted and of the same size as the object (). (b) The ray parallel to the axis diverges as if it came from and the ray through goes straight on; they meet (by backward extension) between and , so the image is formed between the optical centre and the focus on the object's side, nearer the lens than the object - virtual, erect and diminished, as shown in the ray diagram. (c) (i) , so the equivalent focal length is cm and the power is D; the combination acts as a concave (diverging) lens. OR (c) (ii) D (focal length m). The total power is positive, so the combination behaves as a convex (converging) lens, because the convex lens has the shorter focal length and hence the greater power.
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?
    2. (ii)Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?
    3. (iii)Define the S.I. unit of electric current.
    Show answer

    Resistance depends on dimensions, resistivity only on material; alloys have high resistivity and do not oxidise readily; 1 A is 1 C per second.

    (i) Resistance depends on the dimensions of the conductor, , so it changes when the length or the area of cross-section is changed. Resistivity is a characteristic property of the material, depending only on the nature of the material and its temperature; when or changes, changes in the same ratio as , so stays the same. (ii) An alloy has a much higher resistivity than a pure metal, so even a short coil of it has a large resistance, and it is in this high resistance that the heat is produced; also, an alloy does not oxidise (burn) readily at the high temperature at which the element works. (iii) The S.I. unit of electric current is the ampere (A). One ampere is the current when one coulomb of charge flows through any cross-section of a conductor in one second: .
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)How many bulbs of resistance each should be connected in parallel combination to draw a current of 2 A from a battery of 4 V ?
    2. (ii)Name the device used for measuring electric current. How is it connected in a circuit ?
    3. (iii)State Joule's law of heating.
    Show answer

    Four bulbs are needed; current is measured by an ammeter connected in series; Joule's law gives the heat as .

    (i) Four bulbs (). The combination must have resistance , and identical bulbs in parallel have , so ; each bulb draws A, and A. (ii) The device is an ammeter. It is connected in series with the part of the circuit whose current is to be measured, with its positive terminal towards the positive terminal of the battery. (iii) Joule's law of heating: the heat produced in a resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance for a given current, and directly proportional to the time for which the current flows through the resistor; that is, .
    Step-by-step solution →

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