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CBSE Class 10 Science 2025 — Paper 31/6/2

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

31 of its 45 questions also appear in 31/6/1 or 31/6/3; 14 are only in this paper.

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Questions 1–20 · 1 mark each

  1. Q1 1 mark

    Also in 31/6/1 (Q4), 31/6/3 (Q5)

    A Hydrocarbon which does not belong to the same homologous series of carbon compounds is
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (c)
    Step-by-step solution →
  2. Q2 1 mark
    The formula of washing soda is
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/6/1 (Q1)

    In the following experimental setup of electrolysis of water, if P and Q are the gases collected in the test tubes enclosing the electrodes R and S, then select the option/options in which the matching is correct :
    1. (i)P - Oxygen gas , R - Anode
    2. (ii)P - Hydrogen gas , R - Cathode
    3. (iii)Q - Hydrogen gas , S - Cathode
    4. (iv)Q - Oxygen gas , S - Anode
    Battery P Q Test Tube Water R S
    1. (a)(i) and (ii)
    2. (b)(iii) and (iv)
    3. (c)(i) and (iii)
    4. (d)(ii) and (iv)
    Show answer
    (c) (i) and (iii)
    Step-by-step solution →
  4. Q4 1 mark

    Also in 31/6/1 (Q3)

    Select from the following a statement which is not true about burning of magnesium ribbon in air :
    1. (a)It burns with a dazzling white flame.
    2. (b)A white powder is formed on burning.
    3. (c)It is an endothermic reaction.
    4. (d)It is an example of a combination reaction.
    Show answer
    (c) It is an endothermic reaction.
    Step-by-step solution →
  5. Q5 1 mark

    Also in 31/6/1 (Q7), 31/6/3 (Q6)

    The water of crystallization is present in
    1. (i)Bleaching Powder
    2. (ii)Plaster of Paris
    3. (iii)Washing Soda
    4. (iv)Baking Soda
    1. (a)(ii) and (iv)
    2. (b)(ii) and (iii)
    3. (c)(i) and (iii)
    4. (d)(i) and (iv)
    Show answer
    (b) (ii) and (iii)
    Step-by-step solution →
  6. Q6 1 mark
    The nature of aqueous solution of potassium nitrate is :
    1. (a)acidic
    2. (b)basic
    3. (c)neutral
    4. (d)alkaline
    Show answer
    (c) neutral
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/6/1 (Q5), 31/6/3 (Q4)

    The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is
    1. (a)Blue
    2. (b)Pale green
    3. (c)Yellow
    4. (d)Reddish brown
    Show answer
    (b) Pale green
    Step-by-step solution →
  8. Q8 1 mark
    Mendel obtained generation by
    1. (a)self pollinating generation plants
    2. (b)cross pollinating generation plants with plants having dominant trait.
    3. (c)cross pollinating generation plants with plants having recessive trait.
    4. (d)cross pollinating both the parents.
    Show answer
    (a) self pollinating generation plants
    Step-by-step solution →
  9. Q9 1 mark

    Also in 31/6/1 (Q11), 31/6/3 (Q10)

    The basic filtration unit of the excretory system in human beings is :
    1. (a)Nephron
    2. (b)Urethra
    3. (c)Neuron
    4. (d)Urinary bladder
    Show answer
    (a) Nephron
    Step-by-step solution →
  10. Q10 1 mark
    When a seed germinates the root grows downwards and a small shoot grows upward. This shoot is known as
    1. (a)radicle
    2. (b)stem
    3. (c)cotyledon
    4. (d)plumule
    Show answer
    (d) plumule
    Step-by-step solution →
  11. Q11 1 mark

    Also in 31/6/1 (Q9)

    A pair of endocrine glands located in the human brain is
    1. (a)Parathyroid and Pituitary
    2. (b)Pineal and Thymus
    3. (c)Hypothalamus and Thymus
    4. (d)Hypothalamus and Pineal
    Show answer
    (d) Hypothalamus and Pineal
    Step-by-step solution →
  12. Q12 1 mark

    Also in 31/6/1 (Q13), 31/6/3 (Q14)

    Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown :
    C F P C F P (A) C F P (B) C F P (C) C F P (D)
    1. (a)The reflected ray crosses the principal axis between F and the pole P, and runs on below the axis.
    2. (b)The reflected ray crosses the principal axis at the centre of curvature C.
    3. (c)The reflected ray crosses the principal axis at the principal focus F.
    4. (d)The reflected ray travels back to the left above the principal axis without ever meeting it.
    Show answer
    (c) The reflected ray crosses the principal axis at the principal focus F.
    Step-by-step solution →
  13. Q13 1 mark

    Also in 31/6/1 (Q12), 31/6/3 (Q12)

    In human alimentary canal, the digestive juice secreted by the gastric glands are
    1. (a)Bile, Trypsin, Pepsin
    2. (b)Hydrochloric acid, Pepsin, Mucus
    3. (c)Lipase, Bile, Mucus
    4. (d)Salivary amylase, Pepsin, Bile
    Show answer
    (b) Hydrochloric acid, Pepsin, Mucus
    Step-by-step solution →
  14. Q14 1 mark
    Most of the refraction for the light rays entering the eye occurs at
    1. (a)Iris
    2. (b)Pupil
    3. (c)Crystalline lens
    4. (d)Outer surface of Cornea
    Show answer
    (d) Outer surface of Cornea
    Step-by-step solution →
  15. Q15 1 mark

    Also in 31/6/1 (Q16)

    The incorrect statement about ozone is
    1. (a)It is a deadly poisonous gas.
    2. (b)It shields the surface of the earth from UV radiation from sun.
    3. (c)It is used as a refrigerant and in fire-extinguishers.
    4. (d)It is formed by combining oxygen molecule with free oxygen atom.
    Show answer
    (c) It is used as a refrigerant and in fire-extinguishers.
    Step-by-step solution →
  16. Q16 1 mark
    Green plants occupy the first trophic level in every food chain because they
    1. (a)exist over a large area.
    2. (b)have very less concentration of harmful chemicals.
    3. (c)have to feed large number of herbivores.
    4. (d)can synthesize food by photosynthesis.
    Show answer
    (d) can synthesize food by photosynthesis.
    Step-by-step solution →
  17. Q17 1 mark

    Also in 31/6/1 (Q18), 31/6/3 (Q17)

    Two statements are given below – 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) given below.

    Assertion (A): Xylem tissue moves water and minerals obtained from the soil by the roots.

    Reason (R): Xylem tissue is found only in the roots of a plant.

    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 and 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 →
  18. Q18 1 mark

    Also in 31/6/1 (Q20), 31/6/3 (Q19)

    Two statements are given below – 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) given below.

    Assertion (A): Food web is a network of several food chains operating in an ecosystem.

    Reason (R): Food web decreases the stability of an ecosystem.

    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 and 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 →
  19. Q19 1 mark

    Also in 31/6/1 (Q17), 31/6/3 (Q18)

    Two statements are given below – 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) given below.

    Assertion (A): Carbon and its compounds are our major sources of fuels.

    Reason (R): Most of the carbon compounds on burning release a large amount of heat and light.

    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 and 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 →
  20. Q20 1 mark

    Also in 31/6/1 (Q19), 31/6/3 (Q20)

    Two statements are given below – 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) given below.

    Assertion (A): In the common domestic circuits the earth wire is connected to a metallic plate buried deep inside the earth.

    Reason (R): Earth wire ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, so the user may not get a severe electric shock.

    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 and 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 →

Questions 21–26 · 2 marks each

  1. Q21 2 marks
    Cinnabar is an ore of a metal ‘X’. When this ore is heated in air, it is first converted into oxide of ‘X’ (XO) and then reduced to metal ‘X’ on further heating. Identify metal ‘X’ and write chemical equations for the reactions that occur in the above processes.
    Show answer

    X is mercury: roasting cinnabar gives mercury oxide and sulphur dioxide, and heating the oxide further gives mercury and oxygen.

    Metal X is mercury (Hg); cinnabar is mercury(II) sulphide, , and XO is mercury(II) oxide, . Heating the ore in air (roasting): Further heating of the oxide:
    Step-by-step solution →
  2. Q22(a) 2 marks

    Also in 31/6/1 (Q23(a)), 31/6/3 (Q24(a))

    “Proteins control the expression of various characters.” Explain this statement by taking an example of “tallness” as a characteristic in plants.
    Show answer

    Tallness depends on a hormone made by an enzyme (a protein) coded by a gene; an altered gene gives a short plant.

    A gene carries the information for making a protein, so a character can only be expressed through a protein. The height of a plant depends on the amount of plant growth hormone it makes, and that hormone is made by an enzyme, which is a protein. If the gene works efficiently, plenty of the active enzyme is made, plenty of hormone is produced and the plant is tall. If that gene is altered so that the enzyme is less efficient, less hormone is made and the plant remains short. Tallness is therefore controlled by the protein the gene codes for, which is what is meant by saying that proteins control the expression of characters.
    Step-by-step solution →
    OR
    Q22(b) 2 marks

    Also in 31/6/1 (Q23(b)), 31/6/3 (Q24(b))

    Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.
    Show answer

    Gametes carry half the chromosomes and fertilisation restores the full number, so the species' DNA stays stable from generation to generation.

    In sexually reproducing organisms the germ cells, or gametes, are made by a special cell division that halves the chromosome number, so a gamete carries only one set of chromosomes, , while a body cell carries two, . At fertilisation a male gamete fuses with a female gamete, so the zygote receives one set from each parent and the full number is restored. In a human, . The halving and the doubling cancel exactly, so the amount of DNA and the number of chromosomes of the species stay stable from generation to generation, even though each offspring gets a fresh combination of genes.
    Step-by-step solution →
  3. Q23 2 marks

    Also in 31/6/1 (Q22), 31/6/3 (Q25)

    1. (a)How is brain protected in our body ?
    2. (b)A doctor finds in one of his patients that he is not maintaining a proper posture and balance of his body. State the region of brain and also the part of brain which is responsible for it.
    Show answer

    A bony cranium, three meninges and cerebrospinal fluid protect the brain; the cerebellum of the hind-brain maintains posture and balance.

    (a) The brain is protected by a bony box, the cranium of the skull; inside it the brain is covered by three membranes, the meninges, and it is contained in a fluid filled balloon of cerebrospinal fluid, which cushions it against shocks. (b) Region of the brain: the hind-brain. Part responsible: the cerebellum, which maintains posture and balance of the body.
    Step-by-step solution →
  4. Q24(a) 2 marks

    Also in 31/6/1 (Q25(a)), 31/6/3 (Q23(a))

    Give reasons :
    1. (i)The sky appears dark to passengers flying at very high altitude.
    2. (ii)‘Danger’ signal lights are red in colour.
    Show answer

    (i) Thin air at high altitude scatters little light, so the sky looks dark; (ii) red is scattered the least, so it is seen farthest.

    (i) At a very high altitude the atmosphere is extremely thin, so there are very few air molecules and dust particles to scatter sunlight. Hardly any scattered light reaches the passengers' eyes, so the sky appears dark to them instead of blue. (ii) Red light has the longest wavelength of the visible colours, and scattering falls off steeply as the wavelength grows, so red is scattered the least by fog, smoke and dust. It therefore travels the farthest and is visible from the greatest distance, which is what a danger signal needs.
    Step-by-step solution →
    OR
    Q24(b) 2 marks

    Also in 31/6/1 (Q25(b)), 31/6/3 (Q23(b))

    What is a rainbow ? “We see a rainbow in the sky only after the rainfall.” Why ?
    Show answer

    A rainbow is a spectrum formed by dispersion of sunlight in water droplets, so it is seen only after rain.

    A rainbow is a natural spectrum, an arc of seven colours, that appears in the sky after a rain shower. It is caused by the dispersion of sunlight by the tiny water droplets suspended in the atmosphere: each droplet acts as a small prism, so sunlight entering it is refracted and dispersed, then reflected internally at the inner surface at the back of the drop, and refracted again as it leaves. The colours emerge separated, red at about and violet at about to the direction of the sunlight, and the rainbow is always seen opposite the Sun. We see it only after rainfall because only then are tiny water droplets suspended in the air to act as those prisms; without the droplets there is nothing to disperse the sunlight.
    Step-by-step solution →
  5. Q25 2 marks

    Also in 31/6/1 (Q24), 31/6/3 (Q22)

    Study the figure in which the path of a ray of light going from Medium 1 to Medium 2 is shown.
    1. (a)Out of the two Media – Medium 1 and Medium 2, in which is the speed of light more ?
    2. (b)State reason of bending of the refracted ray away from the normal.
    3. (c)Express refractive index of Medium 2 with respect to Medium 1 in terms of speed of light in two media.
    Incident Ray Medium 1 Medium 2 Refracted Ray
    Show answer

    Light is faster in Medium 2; the ray bends away from the normal in the rarer medium; .

    (a) The speed of light is more in Medium 2. (b) The ray bends away from the normal because it passes from an optically denser medium into an optically rarer medium, in which light travels faster; the change of speed at the boundary changes the direction of the ray, so the angle of refraction is greater than the angle of incidence. (c) , where and are the speeds of light in Medium 1 and Medium 2 respectively.
    Step-by-step solution →
  6. Q26 2 marks
    Indicate the flow of energy in a food chain operating in an ecosystem. Why is it uni-directional ? Give reason.
    Show answer

    Energy flows from the Sun to producers, herbivores and carnivores, about passing on each step, and never returns.

    Flow of energy: Sun → producers (green plants) → herbivores (primary consumers) → carnivores (secondary consumers) → top carnivores (tertiary consumers). Green plants capture about 1% of the sunlight falling on their leaves, and on average only about 10% of the energy at one level is passed on to the next; much of the rest is used in life processes or lost to the surroundings as heat. It is uni-directional because the energy captured by the autotrophs does not revert to the solar input, and the energy that passes to the herbivores does not come back to the autotrophs: as it moves progressively through the trophic levels it is no longer available to the previous level.
    Step-by-step solution →

Questions 27–33 · 3 marks each

  1. Q27 3 marks

    Also in 31/6/1 (Q30)

    The gene combination of purple flowered pea plants is denoted as (WW) and that of white flowered pea plants as (ww), when these two plants are crossed generation is obtained.
    1. (a)List two observations made by Mendel in generation plants.
    2. (b)Give the (i) percentage of white flowered plants and (ii) ratio of the gene combinations WW, Ww and ww in generation. (c) Write one difference between dominant and recessive trait.
    Show answer

    All plants were purple with no blending; 25% of plants are white, and .

    (a) All the F1 plants bore purple flowers, so only one of the two parental traits was expressed and not one white flowered plant appeared; and no plant of an intermediate colour was seen, so the two traits had not blended. The white character was not lost but only hidden, as its reappearance in F2 shows: purple is dominant and white recessive, and the F1 plants are Ww although they look like the purple parent. (b) (i) White flowered plants in F2 . (ii) . (c) A dominant trait shows itself when even one copy of its allele is present, as in Ww, whereas a recessive trait shows only when both alleles are recessive, as in ww.
    Step-by-step solution →
  2. Q28(a) 3 marks
    In an experiment a student dipped pH papers in four different solutions A, B, C and D and reported his observation as given below : (i) In which one of these solutions is the concentration of
    1. (1)hydrogen / hydronium ions;
    2. (2)hydroxyl ions maximum ? (ii) Give one example each of the two solutions identified in (i) above. (iii) What would be the pH of the resultant mixture obtained when these two solutions are mixed together in equal proportions ? Justify your answer.
    Colour of pH paper in the four solutions
    SolutionABCD
    Colour of pH paperLight greenBlueGreenRed
    Show answer

    Solution D has most hydrogen ions and B most hydroxyl ions (e.g. HCl and NaOH); mixed to neutralise each other, they give pH 7.

    (i) (1) Solution D (red, lowest pH) has the maximum concentration of hydrogen / hydronium ions. (2) Solution B (blue, basic) has the maximum concentration of hydroxyl ions. (ii) D: dilute hydrochloric acid, . B: sodium hydroxide solution, . (iii) pH 7 — the mixture is neutral. Taken in amounts that exactly neutralise each other, the acid and the base react to form a salt and water, : the hydrogen ions and hydroxyl ions combine to form water, and sodium chloride, the salt of a strong acid and a strong base, is neutral.
    Step-by-step solution →
    OR
    Q28(b) 3 marks
    1. (i)Name the gas liberated when an acid reacts with a metal. How is this gas tested ?
    2. (ii)Write the chemical equation for the reaction of zinc metal with (1) hydrochloric acid, and (2) sodium hydroxide Name the compound of zinc obtained in each case.
    Show answer

    Hydrogen burns with a pop; zinc with hydrochloric acid gives zinc chloride, and with sodium hydroxide gives sodium zincate, each with hydrogen.

    (i) Hydrogen gas. It is tested by bringing a burning matchstick or candle near the gas: it burns with a pop sound. (ii) (1) — the compound of zinc is zinc chloride, . (2) — the compound of zinc is sodium zincate, .
    Step-by-step solution →
  3. Q29 3 marks
    An object of size 5 cm is placed at a distance of 30 cm from the optical centre of a converging lens of focal length 20 cm. Use lens formula to determine the position and size of the image formed.
    Show answer

    The image is real, 60 cm from the optical centre on the other side, and 10 cm tall (inverted).

    Position: cm — the image is formed cm from the optical centre on the other side of the lens, and it is real. Size: cm — the image is cm tall and inverted, twice the size of the object ().
    Step-by-step solution →
  4. Q30 3 marks

    Also in 31/6/1 (Q27)

    Write balanced chemical equation for the reactions that occur when
    1. (a)steam is passed over red hot iron.
    2. (b)natural gas is burnt in air.
    3. (c)glucose reacts with oxygen in the cells of our body and provides energy.
    Show answer

    Balanced equations: iron and steam give and hydrogen, methane burns to and water, and glucose gives , water and energy.

    (a) ; (b) with heat and light; (c) with release of energy.
    Step-by-step solution →
  5. Q31 3 marks

    Also in 31/6/1 (Q33), 31/6/3 (Q33)

    1. (a)Explain the statement "Potential difference between two points is 1 volt".
    2. (b)What do the symbols given below represent in an electric circuit ? Write one function of each.
    A + − (i) (ii)
    Show answer

    1 volt means 1 joule of work per coulomb; the symbols are an ammeter (measures current) and a rheostat (varies current).

    (a) The potential difference between two points is 1 volt when 1 joule of work is done in moving a charge of 1 coulomb from one point to the other; that is, and . (b) (i) An ammeter. It is connected in series in the circuit and measures the electric current flowing through it, its plus terminal being joined towards the positive terminal of the cell. (ii) A variable resistance, that is a rheostat. It is connected in series and is used to change the resistance of the circuit and so to vary the current flowing in it.
    Step-by-step solution →
  6. Q32 3 marks

    Also in 31/6/1 (Q31), 31/6/3 (Q29)

    A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below : Analyse the observation table and on the basis of your analysis only, answer the following questions (without doing any calculations) :
    1. (a)What is the focal length of the convex lens used ? Give reason to justify your answer.
    2. (b)Which one of the sets of observations is not correct and why ?
    3. (c)Draw ray diagram to show image formation for any correct set of observation.
    Observations of the candle flame and its image for a convex lens
    S.No.Distance of flame from the lens (cm)Distance of the image from the lens
    1
    2
    3
    4
    5
    6
    7
    8
    Show answer

    cm, as object and image are both at 30 cm (); set 8 is wrong because the flame is inside the focal length.

    (a) cm. In set 4 the flame and its image are both 30 cm from the lens; for a convex lens the two distances are equal only when the object is at 2F, so cm and cm. (b) Set 8 is not correct. The flame there is 12 cm from the lens, which is less than the focal length of 15 cm, so it lies between the optical centre and the focus. A convex lens then gives a virtual, erect and magnified image on the same side as the flame, which cannot be caught on a screen, so an image distance of cm is impossible. (c) For set 4 the ray diagram shows the object at 2F and a real, inverted image of the same size at 2F on the other side, with cm and .
    Step-by-step solution →
  7. Q33 3 marks
    1. (a)Draw a diagram to show the dispersion of white light by a glass prism.
    2. (b)What is spectrum ? Give reason for its formation.
    Show answer

    A prism splits white light into a spectrum of seven colours, because different colours bend through different angles, red least and violet most.

    (a) The diagram shows a narrow beam of white light falling on one face of a glass prism, splitting into colours inside the prism, and leaving as separate coloured rays bent towards the base, which form a band on a screen with red at the top and violet at the bottom. (b) The band of the coloured components of a light beam is called its spectrum; for white light it is violet, indigo, blue, green, yellow, orange and red (VIBGYOR). It forms because different colours of light bend through different angles as they pass through the prism — red the least and violet the most — since the refractive index of glass is different for different colours; each colour emerges along a different path, and so the colours become distinct.
    Step-by-step solution →

Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks

    Also in 31/6/1 (Q35(a))

    1. (a)Define Puberty. List any two changes seen in boys at the time of puberty.
    2. (b)Why are testes in human males located outside the abdominal cavity in scrotum ?
    3. (c)List any three techniques of contraception used by humans. Which one of these is not meant for males ?
    Show answer

    Puberty is when the reproductive organs mature; the scrotum keeps the testes cooler for sperm formation; oral pills are not meant for males.

    (a) Puberty is the period during adolescence at which the reproductive organs mature and become functional, so that the body becomes capable of sexual reproduction. Two changes seen in boys are the growth of thick hair on the face as a beard and moustache, and in the armpits and pubic region; and the cracking and deepening of the voice as the larynx enlarges. (b) The formation of sperms requires a temperature about two to three degrees Celsius below the normal body temperature. The scrotum, lying outside the abdominal cavity, is cooler than the interior of the body and so provides that lower temperature. (c) Three techniques are the barrier method, such as the condom; the chemical or hormonal method, that is oral contraceptive pills; and the surgical method, that is vasectomy in males or tubectomy in females. Of these, the oral contraceptive pill is not meant for males, since it is taken only by females.
    Step-by-step solution →
    OR
    Q34(b) 5 marks

    Also in 31/6/1 (Q35(b))

    (a) Name the part performing following functions in human female reproductive system :
    1. (i)production of eggs
    2. (ii)site of fertilization
    3. (iii)site of implantation
    4. (iv)entry of the sperms (b) What changes are observed in the uterus : (i) subsequent to implantation of zygote and (ii) if an egg does not get fertilized ?
    Show answer

    The parts are the ovary, fallopian tube, uterus and vagina; the lining thickens after implantation or is shed as menstruation if no fertilisation occurs.

    (a) (i) Ovary; (ii) Fallopian tube, that is the oviduct; (iii) Uterus, in its lining; (iv) Vagina. (b) (i) After the zygote implants, the lining of the uterus becomes still thicker and richer in blood vessels, and a placenta develops between the embryo and the uterine wall, with villi on the embryo's side and blood spaces on the mother's side, through which glucose and oxygen pass to the embryo and its wastes pass back to the mother; the uterus enlarges as the embryo grows. (ii) If the egg is not fertilised, the thick lining is no longer needed and breaks down, and it is shed through the vagina as blood and mucus. This is menstruation, lasting about two to five days and recurring about every twenty-eight days.
    Step-by-step solution →
  2. Q35(a) 5 marks

    Also in 31/6/1 (Q34(a)), 31/6/3 (Q36(a))

    Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid ? Write chemical equations for the reactions involved in the two cases mentioned above.
    Show answer

    Ethanol, , is oxidised to ethanoic acid, ; the two react with an acid catalyst to form the ester ethyl ethanoate and water.

    The alcohol is ethanol, , and the carboxylic acid is ethanoic acid, , in which the second carbon is doubly bonded to one oxygen and singly bonded to an group. Ethanol is converted into ethanoic acid by oxidation, on warming with alkaline potassium permanganate (or acidified potassium dichromate): . When the two compounds are warmed together in the presence of a little concentrated sulphuric acid they undergo esterification, forming ethyl ethanoate, an ester with a sweet fruity smell, and water: .
    Step-by-step solution →
    OR
    Q35(b) 5 marks

    Also in 31/6/1 (Q34(b)), 31/6/3 (Q36(b))

    What are soaps ? Write the structure of a soap molecule. Explain the cleansing action of a soap. Why are soaps not considered suitable for washing clothes in a region where water is hard ? How is this problem overcomed ?
    Show answer

    Soaps are salts of long-chain carboxylic acids that clean by forming micelles; they form scum in hard water, so detergents are used.

    Soaps are the sodium or potassium salts of long-chain carboxylic acids, made by heating a fat or an oil with alkali. A soap molecule, for example sodium stearate , has a long hydrocarbon tail that is hydrophobic and dissolves in oil, and an ionic head that is hydrophilic and dissolves in water. In cleansing, the tails of many molecules enter the oily dirt while the heads remain in the water, so the molecules form a micelle with the dirt trapped inside; agitation frees the micelles from the cloth, they repel one another and remain suspended, and the dirt is rinsed away with the water. Soaps are unsuitable in hard water because hard water contains calcium and magnesium ions, and the calcium and magnesium salts of fatty acids are insoluble: they separate as a white curdy scum, so soap is wasted before any lather forms and the scum sticks to the clothes, as in . The problem is overcome by using detergents, the ammonium or sulphonate salts of long-chain hydrocarbons, whose calcium and magnesium salts are soluble in water, so they lather well even in hard water; the water may also be softened first.
    Step-by-step solution →
  3. Q36(a) 5 marks
    (a) Study the following electric circuit diagram and answer the questions that follow :
    1. (i)What does the circuit diagram shows ?
    2. (ii)What will happen if the direction of current is reversed ? Justify your answer giving circuit diagram. (b) Name and state the rule to determine the direction of magnetic field associated with a straight current carrying conductor.
    K + − N S N East N E S W
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    Current produces a magnetic field, deflecting the compass needle; reversing the current reverses the deflection; the right-hand thumb rule gives the field direction.

    (a) (i) The circuit shows that an electric current flowing through a conductor produces a magnetic field around it. When the key is closed, current flows from north to south in the straight wire laid over the compass, and the north end of the compass needle is deflected towards the East. (ii) If the direction of current is reversed, by reversing the connections of the cells, the current flows from south to north in the wire and the needle is deflected the opposite way, towards the West. The direction of the magnetic field produced by a current depends on the direction of the current, so reversing the current reverses the field. In the circuit diagram the cells are turned round, so every current arrow points the other way. (b) The right-hand thumb rule: imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current; then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field.
    Step-by-step solution →
    OR
    Q36(b) 5 marks
    (a) Draw the pattern of magnetic field lines of
    1. (i)a bar magnet
    2. (ii)a current carrying solenoid List two distinguishing features between the two magnetic fields. (b) Study the following three diagrams in which the entry of an electron in a magnetic field is shown. Identify the case in which the magnetic force experienced by the electron is (i) maximum, and (ii) minimum. Give reason for your answers in each case.
    Electron Magnetic field (A) Electron Magnetic field (B) Electron Magnetic field (C)
    Show answer

    Bar-magnet and solenoid field patterns, the solenoid's being uniform inside; the electron feels maximum force in (A) and minimum in (C).

    (a) (i) Bar magnet: closed field lines that emerge from the north pole, curve round outside and enter the south pole, running from S to N inside the magnet; they never cross and are crowded near the poles. (ii) Current-carrying solenoid: parallel, equally spaced straight lines inside, along the axis; outside, a pattern like that of a bar magnet, one end acting as a north pole and the other as a south pole. Two distinguishing features: (1) Inside a solenoid the field is uniform — its field lines are parallel and equally spaced — whereas the field lines around a bar magnet curve and crowd together near the poles, so that field is non-uniform. (2) A solenoid’s field exists only while current flows, and its strength and direction can be changed by changing or reversing the current (or by changing the number of turns); a bar magnet’s field is permanent and fixed. (b) (i) Maximum force in (A): the electron moves at right angles to the magnetic field. (ii) Minimum force in (C): the electron moves along the field lines, opposite to the field, so it experiences no magnetic force at all. The force on a moving charge, as on a current, is greatest when its motion is perpendicular to the field and zero when it is parallel or opposite to the field; in (B) it moves at an angle, so the force lies in between.
    Step-by-step solution →

Questions 37–39 · 4 marks each

  1. Q37 4 marks

    Also in 31/6/1 (Q37), 31/6/3 (Q37)

    Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
    1. (I)How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it ?[1]
    2. (II)Name an alloy used for welding two wires together in an electric circuit. Write its major constituents.[1]
    3. (III)(a)What are alloys ? How is ‘Brass’ (an alloy) prepared ?[2]
    4. (III)(b)OR : What is stainless steel ? How is it prepared ? Write one important property which makes it more useful in making cooking utensils as compared to its primary metal.[2]
    Show answer

    Alloying lowers conductivity and melting point; solder is lead and tin; brass is copper and zinc; stainless steel does not rust.

    (I) Both decrease: the electrical conductivity of the alloy is less than that of the pure metal, and so is its melting point. (II) Solder; its major constituents are lead (Pb) and tin (Sn), about half and half by mass. (III)(a) An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Brass is made by melting copper and dissolving the required amount of zinc in the molten copper (about Cu and Zn), then cooling it. (III)(b) Stainless steel is an alloy of iron with chromium and nickel. It is made by melting iron and mixing in about chromium and nickel, then cooling. It does not rust or corrode, unlike pure iron, which is what makes it better for cooking utensils.
    Step-by-step solution →
  2. Q38 4 marks

    Also in 31/6/1 (Q38), 31/6/3 (Q38)

    The growth movements of plant parts in which the direction of the stimulus determines the direction of the response is known as tropic movements or tropism. Plants also have non-directional movements which may not be growth dependent.
    Potted plant lying on its side with roots X and shoot Y X Y
    1. (I)Name the movement which causes ‘X’ and ‘Y’ to grow downwards and upwards respectively. (Refer above figure)[1]
    2. (II)Write the name of a hormone that plays a major role in (i) falling of leaves (ii) rapid cell division[1]
    3. (III)(a)Leaves of the sensitive plant move very quickly in response to ‘touch’. How is this stimulus of touch communicated and explain how the movement takes place.[2]
    4. (III)(b)OR : Name the plant hormone which is synthesized at the shoot tip. How does this hormone helps the plant to bend towards light ?[2]
    Show answer

    Geotropism; abscisic acid and cytokinin; touch-sensitive leaves fold by losing water; auxin bends shoots towards light.

    (I) Geotropism (gravitropism): the root X shows positive geotropism by growing towards gravity and the shoot Y shows negative geotropism by growing away from it. (II) (i) Abscisic acid; (ii) Cytokinin. (III)(a) Plants have no nerves, so the touch is passed from cell to cell as an electrical and chemical signal. The cells at the base of the leaflets then lose water, shrink and lose their swollen shape, so the leaflets fold and droop; when water returns they swell again and the leaflets reopen. The movement is not caused by growth. (III)(b) Auxin. Made at the shoot tip, it diffuses towards the shaded side when light comes from one side. The cells on that shaded side then grow longer than those on the lit side, and this unequal growth bends the shoot towards the light.
    Step-by-step solution →
  3. Q39 4 marks

    Also in 31/6/1 (Q39), 31/6/3 (Q39)

    Study the circuit shown in which two resistors X and Y of resistances and respectively are joined in series with a battery of V.
    Series circuit printed with question 39 X 3 Ω 6 Ω Y V − + A − + − + 2V
    1. (I)Draw a circuit diagram showing the above two resistors X and Y joined in parallel with same battery and same ammeter and voltmeter.[1]
    2. (II)In which combination of resistors will the (i) potential difference across X and Y and (ii) current through X and Y, be the same ?[1]
    3. (III)(a)Find the current drawn from the battery by the series combination of the two resistors (X and Y).[2]
    4. (III)(b)OR : Determine the equivalent resistance of the parallel combination of the two resistors (X and Y).[2]
    Show answer

    Parallel gives equal potential difference and series gives equal current; the series current is A, or the parallel resistance is .

    (I) X and Y are drawn as two separate branches between the same pair of junctions, with the V battery and the plug key in the main circuit, the ammeter still in the main line and the voltmeter connected across the parallel pair (see the circuit diagram). (II) (i) The potential difference across X and Y is the same in the parallel combination; (ii) the current through X and Y is the same in the series combination. (III)(a) , so the current drawn is A. (III)(b) , so .
    Step-by-step solution →

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