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CBSE Class 10 Science 2026 — Paper 31/2/3

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

32 of its 45 questions also appear in 31/2/1 or 31/2/2; 13 are only in this paper.

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Questions 1–9 · 1 mark each

  1. Q1 1 mark

    Also in 31/2/1 (Q4)

    The carbohydrates, which are not used immediately in plants, are stored in the form of ‘a’, which serves as an internal energy reserve. What does ‘a’ stand for ?
    1. (a)Starch
    2. (b)Sugar
    3. (c)Fat
    4. (d)Protein
    Show answer
    (a) Starch
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/2/1 (Q3), 31/2/2 (Q1)

    Spirogyra, despite being a multi-cellular organism, still shows a simple reproductive method. Select the correct option with regard to reproduction in Spirogyra :
    1. (a)Asexual reproduction by division of cells into two cells
    2. (b)Sexual reproduction by division of cells into many cells
    3. (c)Asexual reproduction by breaking up of Spirogyra filaments into smaller parts
    4. (d)Sexual reproduction by the formation of gametes after meiosis of cells of filaments followed by fusion of male and female gametes
    Show answer
    (c) Asexual reproduction by breaking up of Spirogyra filaments into smaller parts
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/2/1 (Q2), 31/2/2 (Q3)

    Identify the type of tropic movement that is responsible for the movement of the pollen tube towards an ovule from the following options.
    1. (a)Hydrotropism
    2. (b)Geotropism
    3. (c)Chemotropism
    4. (d)Phototropism
    Show answer
    (c) Chemotropism
    Step-by-step solution →
  4. Q4 1 mark

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

    The genotype of green stemmed tomato plant is denoted by ‘GG’ and that of purple stemmed tomato plant as ‘gg’. Hybrid of a cross between these two were self-pollinated to obtain progeny. What will be the ratio of GG, Gg and gg in this progeny ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  5. Q5 1 mark
    Select the option that represents the correct balanced equation for the process of photosynthesis :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  6. Q6 1 mark

    Also in 31/2/1 (Q7), 31/2/2 (Q5)

    Which of the following limits the number of trophic levels in a food chain ?
    1. (a)Availability of water
    2. (b)Deficient food supply
    3. (c)Decrease in energy at higher levels
    4. (d)Pollution in air
    Show answer
    (c) Decrease in energy at higher levels
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/2/1 (Q6), 31/2/2 (Q7)

    In the given figure, identify the trophic level having maximum concentration of harmful chemicals.
    T5 T4 T3 T2 T1
    1. (a)T1
    2. (b)T5
    3. (c)T4
    4. (d)T3
    Show answer
    (b) T5
    Step-by-step solution →
  8. Q8 1 mark

    Also in 31/2/1 (Q8), 31/2/2 (Q9)

    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): Blood plasma transports carbon dioxide in dissolved form, while oxygen is transported by respiratory pigments.

    Reason (R): Carbon dioxide is more soluble in water than in oxygen.

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

    Also in 31/2/1 (Q9), 31/2/2 (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): There are generally a greater number of individuals at the lower trophic levels of an ecosystem.

    Reason (R): The greatest number is of the producers.

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

Questions 10–12 · 2 marks each

  1. Q10(a) 2 marks

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

    “The timing and the amount of hormone secreted by a gland are regulated in the human body.” Justify this statement with the help of an example.
    Show answer

    Feedback mechanisms regulate hormone release; for example, rising blood sugar makes the pancreas release more insulin and falling sugar reduces it.

    The timing and the amount of hormone released are regulated by feedback mechanisms. Example: when the sugar level in the blood rises, it is detected by the cells of the pancreas, which respond by producing more insulin; as the blood sugar level falls, insulin secretion is reduced. The hormone is therefore released when it is needed and in the amount needed.
    Step-by-step solution →
    OR
    Q10(b) 2 marks

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

    Electrical impulse is an excellent means to transmit information in the animal body, but there are some limitations to the use of electrical impulses. State any two limitations.
    Show answer

    Impulses reach only cells connected by nervous tissue, and a cell needs time to reset before it can generate a new impulse.

    1. Electrical impulses reach only those cells that are connected by nervous tissue, not each and every cell in the animal body. 2. Once an electrical impulse has been generated and transmitted, the cell takes some time to reset its mechanisms before it can generate and transmit a new impulse, so cells cannot continually create and transmit electrical impulses.
    Step-by-step solution →
  2. Q11 2 marks

    Also in 31/2/2 (Q11)

    Do all variations in a species have equal chances of surviving in the environment in which they find themselves ? Explain.
    Show answer

    No; individuals with variations beneficial in that environment survive, e.g. heat-resistant bacteria when the water warms.

    No. Depending on the nature of their variations, different individuals have different kinds of advantages in a given environment, so variations do not have equal chances of survival: individuals with variations that are beneficial for survival in that environment survive and pass those variations on to their progeny. For example, if a population of bacteria lived in temperate waters and the water temperature rose because of global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Similarly, in a population of red beetles living on green bushes, a green variant cannot be seen by crows, so it survives and leaves more offspring. This selection of variants by environmental factors forms the basis of evolution.
    Step-by-step solution →
  3. Q12 2 marks
    Suggest one precaution to be taken before disposing of the following :
    1. (a)Sewage from homes
    2. (b)Industrial wastes
    Show answer

    Fit a sieve at the drain opening to keep solid waste out of sewage; give industrial wastes chemical treatment before disposal.

    (a) Sewage from homes: Sewage should not carry solid waste, so a sieve should be installed at the opening of the drain. Treating the sewage in a sewage treatment plant before it is discharged into a river is another valid precaution. (b) Industrial wastes: They should be given chemical treatment before disposal, to remove or neutralise their harmful chemicals (for example, neutralise acids and alkalis and remove toxic metals).
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks
    1. (a)Draw a neat diagram of the human respiratory system and label its lungs, trachea, bronchi and alveoli.
    2. (b)State the roles of the following in the process of respiration : (i) Alveoli (ii) Respiratory pigments
    Show answer

    Alveoli are the site of gas exchange, and haemoglobin carries oxygen from the lungs to the tissues.

    (a) See the labelled diagram: the trachea, held open by rings of cartilage, divides into two bronchi, one entering each lung; inside the lungs the bronchi branch into bronchioles, which end in clusters of alveoli. The lungs lie in the chest cavity above the diaphragm. (b) (i) Alveoli: They are the site of exchange of gases. Oxygen from the air in the alveoli diffuses into the blood in the surrounding capillaries, and carbon dioxide diffuses from the blood into the alveoli to be breathed out. Their very large number gives a very large surface for this exchange. (ii) Respiratory pigments: Haemoglobin, present in the red blood cells, has a very high affinity for oxygen. It takes up oxygen from the air in the lungs and carries it to the tissues that are short of oxygen, where it releases it.
    Step-by-step solution →
  2. Q14 3 marks

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

    1. (a)Giving two examples, justify the statement that the sex of the offspring in all animals is not always genetically determined.
    2. (b)Differentiate between the sex chromosomes of male and female human beings.
    Show answer

    Sex can be set by egg temperature (turtles) or by changing sex (snails); females have and males sex chromosomes.

    (a) Sex is not always decided by genes. First, in some reptiles, such as many turtles, the temperature at which the fertilised eggs are incubated decides whether the young develop into males or females. Second, in snails an individual can change its sex during its life. In both cases sex is decided or changed after fertilisation, so it is not fixed by the genes inherited. (b) Human females have a perfect (matched) pair of sex chromosomes, both X, so they are XX. Human males have a mismatched pair, one normal-sized X and one short Y, so they are XY. Hence all eggs carry X, while half the sperms carry X and half carry Y.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks

    Also in 31/2/1 (Q15), 31/2/2 (Q16)

    Read the following passage and answer the questions that follow : A middle-aged person is facing some cognitive changes in himself. His early symptoms included mild forgetfulness. For example, forgetting where he left his mobile or failing to find words to complete his sentences. He was facing problems in driving a car, climbing up and down the stairs, inserting a plug into an outlet. He slowly developed a sad mood and anxiety.
    1. (a)What are voluntary actions ?[1]
    2. (b)Which part of the brain is responsible for precision of voluntary actions ?[1]
    3. (c)(i)Explain the role of the medulla.[2]
    4. (c)(ii)OR : How do the animal muscles move ?[2]
    Show answer

    Voluntary actions are done by will; the cerebellum gives precision; the medulla controls involuntary actions; muscle proteins change shape and the muscle contracts.

    (a) Voluntary actions are actions we perform consciously, by our own will after thinking, such as writing, talking, walking or driving; they are controlled by the fore-brain (cerebrum). (b) The cerebellum (in the hind-brain) is responsible for the precision of voluntary actions; it also maintains the posture and balance of the body. (c)(i) The medulla, in the hind-brain, joins the brain to the spinal cord and controls involuntary actions such as blood pressure, salivation and vomiting (it also helps to regulate the heartbeat and breathing). OR (c)(ii) Muscle cells contain special proteins that, in response to a nerve impulse, change their shape and their arrangement in the cell. This gives the muscle cells a shorter form, so the muscle contracts and moves the part of the body; it relaxes again when the impulses stop.
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks

    Also in 31/2/1 (Q16(a)), 31/2/2 (Q15(a))

    1. (i)Name an organ that helps in the formation of male germ cells in humans and also mention the condition that favours the formation of male germ cells.
    2. (ii)In male reproductive system, write the pathway followed to deliver male germ cells to the site of fertilisation.
    3. (iii)Mention the main physical feature of the male germ cell that helps it move towards the female germ cell.
    Show answer

    The testes need a temperature below body temperature; sperms travel testis, vas deferens, urethra, vagina, uterus and oviduct, helped by the long tail.

    (i) Testes. Sperm formation needs a temperature lower than the normal body temperature, so the testes lie outside the abdominal cavity, in the scrotum, which is about to cooler than the inside of the body. (The testes also secrete the hormone testosterone, which regulates the formation of sperms.) (ii) In the male reproductive system: Testis vas deferens (sperm duct) urethra, the common passage for urine and sperms, through the penis. Along the vas deferens the seminal vesicles and prostate gland add fluid that carries and nourishes the sperms. The sperms are deposited in the vagina and swim through the cervix and uterus to the oviduct (fallopian tube), where fertilisation takes place. (iii) The long tail of the sperm, which helps it swim towards the female germ cell.
    Step-by-step solution →
    OR
    Q16(b) 5 marks

    Also in 31/2/1 (Q16(b)), 31/2/2 (Q15(b))

    Radha has three children. She does not want to have more children. Radha visits a nearby hospital, to know the methods to prevent pregnancy.
    1. (i)Mention the name of any two ways other than the surgical methods, following which Radha can avoid unwanted pregnancies.
    2. (ii)Name the surgical methods to prevent pregnancy.
    3. (iii)Give one example each of sexually transmitted diseases caused by bacteria and virus.
    Show answer

    Radha can use oral pills or condoms; the surgical methods are vasectomy and tubectomy; gonorrhoea is a bacterial and HIV-AIDS a viral STD.

    (i) Any two of: oral contraceptive pills, which change the hormonal balance so that eggs are not released; a copper-T (or loop) placed in the uterus; barrier methods such as a condom on the penis or a similar covering worn in the vagina, which stop the sperms from reaching the egg. (ii) Vasectomy, in which the vas deferens of the male is blocked so that sperms are not transferred; and tubectomy, in which the fallopian tubes of the female are blocked so that the egg cannot reach the uterus. (iii) Caused by bacteria: gonorrhoea (or syphilis); caused by a virus: HIV-AIDS (or warts).
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark
    Tomato is a natural source of which acid ?
    1. (a)Acetic acid
    2. (b)Tartaric acid
    3. (c)Oxalic acid
    4. (d)Citric acid
    Show answer
    (c) Oxalic acid
    Step-by-step solution →
  2. Q18 1 mark
    Which of the following compounds is used for removing permanent hardness of water ?
    1. (a)Bleaching powder
    2. (b)Washing soda
    3. (c)Baking soda
    4. (d)Caustic soda
    Show answer
    (b) Washing soda
    Step-by-step solution →
  3. Q19 1 mark
    Which of the following are decomposition reactions ?
    1. (i)
    2. (ii)
    3. (iii)
    4. (iv) Options :
    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. Q20 1 mark

    Also in 31/2/1 (Q18), 31/2/2 (Q20)

    A metal carbonate reacts with a solution X which forms a salt, water and a gas Y. What are X and Y ?
    1. (a)X – Sodium hydroxide, Y – Carbon dioxide
    2. (b)X – Sodium hydroxide, Y – Hydrogen
    3. (c)X – Hydrochloric acid, Y – Carbon dioxide
    4. (d)X – Hydrochloric acid, Y – Hydrogen
    Show answer
    (c) X – Hydrochloric acid, Y – Carbon dioxide
    Step-by-step solution →
  5. Q21 1 mark

    Also in 31/2/1 (Q19), 31/2/2 (Q23)

    When ferrous sulphate crystals are heated in a test tube, we observe that :
    1. (a)A colourless gas with no smell is evolved.
    2. (b)A brown gas is evolved.
    3. (c)The green colour of the salt fades and a gas with the smell of burning sulphur is evolved.
    4. (d)The green colour of the salt fades and no gas is evolved.
    Show answer
    (c) The green colour of the salt fades and a gas with the smell of burning sulphur is evolved.
    Step-by-step solution →
  6. Q22 1 mark

    Also in 31/2/1 (Q23), 31/2/2 (Q22)

    A student notices that her silver jewellery turned dull and had a grey-black coating over it after wearing for a few months. What results in the change in colour of the silver metal ?
    1. (a)The polish over the jewellery was removed after wearing for a few months.
    2. (b)The jewellery comes in contact with air, moisture and acids and corrodes.
    3. (c)Dust particles over the jewellery change its colour.
    4. (d)Its colour changes due to rusting.
    Show answer
    (b) The jewellery comes in contact with air, moisture and acids and corrodes.
    Step-by-step solution →
  7. Q23 1 mark

    Also in 31/2/1 (Q20), 31/2/2 (Q21)

    When Mg metal is treated with hot water, it starts floating on the surface of the water. The reason for its different behaviour is :
    1. (a)Mg is a lighter element than water.
    2. (b)Mg reacts with water to produce gas which helps in floating.
    3. (c)Mg reacts with water to produce gas which helps in floating.
    4. (d)Mg reacts with water to form gas which helps in floating.
    Show answer
    (b) Mg reacts with water to produce gas which helps in floating.
    Step-by-step solution →
  8. Q24 1 mark
    For Question number 24, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Carbon shows the property of catenation.

    Reason (R): This is due to strong C – C bond.

    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
    Write balanced equations for the reactions of the following :
    1. (a)Iron with steam
    2. (b)Calcium with water
    Show answer

    Iron with steam gives and hydrogen; calcium with water gives and hydrogen.

    (a) Iron with steam: (b) Calcium with water:
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26(a) 3 marks

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

    1. (i)Write one example each of one metal that is so soft that it can be cut with a knife, and one non-metal that is a good conductor of electricity.
    2. (ii)Using the electronic configuration, explain how Mg atom combines with oxygen to form magnesium oxide by transfer of electrons. [Atomic number : , ]
    Show answer

    Sodium is soft enough to cut and graphite conducts; Mg gives two electrons to O, forming ionic .

    (i) Sodium is so soft that it can be cut with a knife (potassium or lithium would also do); graphite, a form of carbon, is a non-metal that is a good conductor of electricity. (ii) The electronic configuration of Mg () is and that of O () is . Magnesium loses its two valence electrons to form (), and oxygen gains these two electrons to form (), so both reach the stable configuration of neon: and . The oppositely charged ions are held together by strong electrostatic attraction, an ionic bond, forming magnesium oxide, ().
    Step-by-step solution →
    OR
    Q26(b) 3 marks

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

    Give reasons :
    1. (i)Metal sulphides and carbonates should be converted to their metal oxides in the process of extraction of metals.
    2. (ii)Aluminium oxide is considered as an amphoteric oxide.
    3. (iii)Metals like Na, K, Ca and Mg are never found in their free state in nature.
    Show answer

    Oxides are easier to reduce; aluminium oxide reacts with both acids and bases; Na, K, Ca and Mg are too reactive to occur free.

    (i) It is easier to obtain a metal from its oxide than from its sulphide or carbonate, because a reducing agent such as carbon works by removing oxygen. So sulphide ores are first roasted, , and carbonate ores calcined, , and the oxide is then reduced, . (ii) Aluminium oxide reacts with both acids and bases to form a salt and water, so it shows both basic and acidic behaviour: and . (iii) Na, K, Ca and Mg are highly reactive metals at the top of the reactivity series. They react readily with oxygen, water and other substances in the environment, so they are always found combined, as compounds, and never in the free state.
    Step-by-step solution →
  2. Q27 3 marks
    Define the following terms :
    1. (a)Corrosion
    2. (b)Rancidity
    3. (c)Double displacement reaction
    Show answer

    Corrosion is attack on a metal by moisture and acids; rancidity is oxidation of fats and oils; double displacement is exchange of ions.

    (a) Corrosion: When a metal is attacked by substances around it, such as moisture and acids, it is said to corrode, and this process is called corrosion. Example: rusting of iron. (b) Rancidity: When fats and oils are oxidised, they become rancid and their smell and taste change. This is called rancidity. (c) Double displacement reaction: A reaction in which there is an exchange of ions between the reactants is called a double displacement reaction. Example: .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks

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

    Read the following passage and answer the questions that follow : In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance ‘Z’ is produced, along with the evolution of gases ‘X’ and ‘Y’. When a burning matchstick is brought near the gas ‘Y’, it burns with a pop sound, whereas ‘X’ is used for disinfecting drinking water. When ‘X’ is passed through slaked lime, an insoluble substance ‘A’ is produced.
    Anode Cathode X Y Brine Z Cl− OH− Na+ H+ Membrane
    1. (a)Write the names of the gases ‘X’ and ‘Y’.[1]
    2. (b)Write the balanced chemical equation for the formation of substance ‘Z’.[1]
    3. (c)(i)What happens : (I) If a drop of red litmus solution is added to the aqueous solution of substance ‘Z’ ? (II) If gas is passed through ammoniacal solution of aqueous NaCl ?[2]
    4. (c)(ii)OR : Identify the substance ‘A’ and write the balanced chemical equation of the reaction which takes place in its preparation.[2]
    Show answer

    X is chlorine, Y hydrogen, Z sodium hydroxide; red litmus turns blue; with ammoniacal brine gives baking soda; A is bleaching powder.

    (a) ‘X’ is chlorine gas, , given off at the anode; ‘Y’ is hydrogen gas, , given off at the cathode. (b) ‘Z’ is sodium hydroxide, formed in the electrolysis of brine (chlor-alkali process): (c)(i) (I) The red litmus turns blue, because sodium hydroxide is a base (an alkali). (II) Sodium hydrogencarbonate (baking soda) is formed and, being sparingly soluble, separates out as a white solid, together with ammonium chloride: OR (c)(ii) ‘A’ is bleaching powder (calcium oxychloride, ), made by passing chlorine over dry slaked lime:
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks

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

    A carbon compound ‘P’ of molecular formula is found to be neutral when tested with red and blue litmus. A gas that burns with a pop sound is produced when sodium metal reacts with compound ‘P’.
    1. (i)Identify the compound ‘P’.
    2. (ii)The carbon compound ‘P’ is heated with conc. at 443 K to produce compound ‘Q’. (I) Write the chemical equation for the reaction. (II) What is the role of conc. in this reaction ?
    3. (iii)What is likely to be observed on heating compound ‘P’ with ethanoic acid with an acid as a catalyst ? Write the chemical equation for the reaction.
    Show answer

    P is ethanol; heated with conc. sulphuric acid at 443 K it dehydrates to ethene (Q); with ethanoic acid it forms a sweet-smelling ester.

    (i) ‘P’ is ethanol, (). It is neutral to litmus, and sodium releases hydrogen from it, the gas that burns with a pop sound. (ii) (I) ; ‘Q’ is ethene. (II) Concentrated sulphuric acid acts as a dehydrating agent: it removes water from ethanol. (iii) A sweet-smelling (fruity) substance, the ester ethyl ethanoate, is formed (esterification):
    Step-by-step solution →
    OR
    Q29(b) 5 marks

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

    1. (i)Write the structural formula of benzene.
    2. (ii)State the reason why carbon can neither form cation nor anion.
    3. (iii)What type of bond is formed between carbon and hydrogen ?
    4. (iv)How is ethanol converted to ethanoic acid ?
    5. (v)Complete the following chemical equation :
    Show answer

    Benzene is a hexagonal ring of six carbons; carbon forms covalent bonds; ethanol is oxidised to ethanoic acid; the ester gives sodium ethanoate and ethanol.

    (i) Benzene, : a hexagonal ring of six carbon atoms joined by alternate single and double bonds, with one hydrogen atom joined to each carbon (drawn in the figure at step 1). (ii) Carbon has four valence electrons (configuration ). To form it would have to gain four electrons, and its nucleus of six protons cannot easily hold ten electrons; to form it would have to lose four electrons, which needs a very large amount of energy. So carbon shares its valence electrons and forms covalent bonds instead. (iii) A covalent bond: a single covalent bond, formed by sharing one pair of electrons between carbon and hydrogen. (iv) By oxidation: ethanol is heated with alkaline potassium permanganate (or acidified potassium dichromate): (v) (sodium ethanoate and ethanol; the reaction is saponification).
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark

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

    From the following options choose the one which gives negative magnification greater than one :
    1. (a)Concave mirror; Nature of image – real
    2. (b)Concave mirror; Nature of image – virtual
    3. (c)Convex mirror; Nature of image – real
    4. (d)Convex mirror; Nature of image – virtual
    Show answer
    (a) Concave mirror; Nature of image – real
    Step-by-step solution →
  2. Q31 1 mark

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

    A thin beam of white light falls on a face of a glass prism and a spectrum is obtained on a screen. Which of the following options is the correct sequence of colours from top to bottom on the screen ?
    1. (a)Red, Green, Yellow, Violet, Blue
    2. (b)Red, Yellow, Green, Blue, Violet
    3. (c)Violet, Blue, Green, Yellow, Red
    4. (d)Violet, Red, Green, Yellow, Blue
    Show answer
    (b) Red, Yellow, Green, Blue, Violet
    Step-by-step solution →
  3. Q32 1 mark

    Also in 31/2/1 (Q32), 31/2/2 (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): Direction of force exerted on a current-carrying conductor placed in a magnetic field remains same if the directions of both magnetic field and current flowing through the conductor are reversed.

    Reason (R): The direction of force exerted on a current-carrying conductor placed in an external magnetic field can be determined by using magnetic compass.

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

Questions 33–34 · 2 marks each

  1. Q33 2 marks
    With the help of above given ray diagram, calculate the angle of refraction. Given that the refractive index of Medium 2 with respect to Medium 1 is .
    Medium 1 Medium 2 A 30° O B
    Show answer

    The angle of refraction is .

    By Snell's law, . The angle of incidence is , so and the angle of refraction is .
    Step-by-step solution →
  2. Q34(a) 2 marks

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

    How does the focal length of eye lens change as the distance of the object from the eyes is altered ? Explain.
    Show answer

    The focal length of the eye lens decreases for nearer objects and increases for farther ones, so the image stays on the retina.

    The focal length of the eye lens decreases as the object is brought nearer and increases as the object moves farther away. The image must always form on the retina, whose distance from the lens is fixed, so the eye adjusts the lens itself (power of accommodation). For a distant object the ciliary muscles relax, the lens becomes thin and its focal length increases; for a near object the ciliary muscles contract, the lens becomes thicker and its focal length decreases, so the image of the near object still falls on the retina.
    Step-by-step solution →
    OR
    Q34(b) 2 marks

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

    Why is the concave lens used as a corrective lens for a myopic eye ?
    Show answer

    A concave lens makes rays from a distant object appear to come from the far point, so the eye focuses them on the retina.

    In a myopic (near-sighted) eye the image of a distant object is formed in front of the retina, because the eye lens is too converging or the eyeball is too long, so the far point is nearer than infinity. A concave lens is a diverging lens: a concave lens of suitable power (focal length equal to minus the far-point distance) spreads out the parallel rays from a distant object so that they appear to come from the far point of the eye. The eye can focus them on the retina, so the distant object is seen clearly. That is why a concave lens is used to correct myopia.
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks
    1. (a)Write the name of the lens and position of the object in front of it so that a virtual and magnified image is formed.
    2. (b)An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. If object is located at 30 cm from this lens, using lens formula find out the position and nature of the image formed.
    Show answer

    Convex lens, object between and ; cm, a real, inverted image twice the size of the object.

    (a) A convex lens, with the object placed between its principal focus and its optical centre (nearer to the lens than its focal length); the image is then virtual, erect and magnified, on the same side as the object. (b) With cm and cm, , so cm: the image is formed cm from the lens on the other side (beyond ). It is real and inverted, and twice the size of the object ().
    Step-by-step solution →
  2. Q36 3 marks

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

    What is scattering of light ? How is scattering of light different from reflection of light ? Explain.
    Show answer

    Scattering sends light in all directions from tiny particles in its path; reflection turns it back from a surface in one direction.

    Scattering of light is the sending out of light in all directions by very small particles in its path - molecules of air, fine dust, smoke or colloidal particles. The colour of the scattered light depends on the size of the particles: very fine particles scatter blue light much more than red, which is why the clear sky looks blue, while larger particles scatter all colours about equally, which is why clouds look white. It differs from reflection in three ways: 1. Scattering is caused by tiny particles in the path of the light; reflection takes place at a surface, such as a mirror. 2. Scattered light spreads out in all directions; light reflected from a smooth surface leaves in one definite direction, fixed by the laws of reflection (the angle of reflection equals the angle of incidence). 3. Scattering depends on the colour (wavelength) of the light, so fine particles can separate blue from red; a mirror reflects every colour in the same direction, so a white beam stays white.
    Step-by-step solution →
  3. Q37 3 marks

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

    The values of current flowing in a given resistor for the corresponding values of potential difference applied across the ends of resistor are given below in the table : Plot a graph between and and calculate the resistance of that resistor.
    (Amperes)0.40.81.21.62.0
    (Volts)1.22.43.64.86.0
    Show answer

    The graph is a straight line through the origin; its slope gives the resistance .

    Plotting (vertical axis) against (horizontal axis) gives a straight line through the origin, so the resistor obeys Ohm's law. Its resistance is the slope of the line: . The resistance of the resistor is .
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks

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

    Read the following passage and answer the questions that follow : Swati, a class 10 student, observes that when she passes close to the refrigerator in her kitchen, she feels the heat, although the things kept inside the refrigerator are cool.
    1. (a)Describe the cause of heating in the above-mentioned case.[1]
    2. (b)A current flows through a resistor of resistance when the potential difference across it is . Applying Ohm's law, write the formula for amount of heat produced by the resistor in time .[1]
    3. (c) (i)Write any two practical applications of heating effect of electric current.[2]
    4. (c) (ii)OR : Define the commercial unit of electric energy and express it in Joules (J).[2]
    Show answer

    The fridge warms the kitchen air by the heating effect of current, ; irons and bulbs use it; or J.

    (a) The heating is caused by the heating effect of electric current. The refrigerator runs on electricity, and its current-carrying parts - the windings of the compressor motor and the connecting wires - have resistance, so part of the electrical energy they draw is continuously converted into heat, which is given out into the kitchen air near the refrigerator. (b) The heat produced is . By Ohm's law , so (equivalently ). (c) (i) Any two of these: the electric iron, toaster, room heater, kettle and geyser, whose resistive heating elements get hot; the electric bulb, whose filament becomes so hot that it glows; the electric fuse, whose wire melts and breaks the circuit when too large a current flows. OR (c) (ii) The commercial unit of electric energy is the kilowatt hour (kWh), the energy used by an appliance of power kW in hour: J.
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)The magnetic field lines due to two bar magnets X and Y are shown in the given diagram. If the magnet X is displaced towards magnet Y, will there be repulsion or attraction between them ? Justify.
    2. (ii)A metallic conductor is suspended perpendicular to the magnetic field of a horseshoe magnet. The conductor gets displaced towards the left when a current is passed through it. What will be the effect on displacement of conductor if the : (I) Current through the conductor is increased ? (II) Horseshoe magnet is replaced by another stronger horseshoe magnet ? (III) Direction of current through the conductor is reversed ?
    X Y
    Show answer

    Repulsion, as the facing ends are both north poles; more current or a stronger magnet increases the displacement, and reversed current reverses it.

    (i) There will be repulsion. Field lines come out of a north pole and go into a south pole; in the diagram they come out of X at its right end and out of Y at its left end, so the two ends facing each other are both north poles, and like poles repel. (ii) (I) The displacement increases, still towards the left, because a larger current increases the force on the conductor. (II) The displacement increases, still towards the left, because a stronger magnet gives a stronger magnetic field and hence a larger force. (III) The conductor is displaced towards the right, because reversing the current reverses the direction of the force (Fleming's left-hand rule); the size of the displacement is unchanged.
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)Draw a schematic diagram of a domestic electric circuit which includes the following devices : (I) A fuse (II) A power meter (III) One light point (IV) A power plug
    2. (ii)Why is it necessary to connect an earth wire to the electrical appliances having metallic covers ?
    Show answer

    The mains pass through fuse, meter and switch to parallel circuits; the earth wire prevents severe shock from a metal cover.

    (i) In the schematic, the live wire (red) and the neutral wire (black) from the pole pass through the main fuse (in the live wire) and the power meter (kWh meter), then through the main switch to the distribution box. From there separate circuits run in parallel, each with its own fuse in the live wire: a A circuit to the light point, with its switch in the live wire, and a A circuit to the power plug (a three-pin socket), with its switch in the live wire and its third pin joined to the earth wire (green), which ends at a metal plate buried in the ground. (ii) If the live wire touches the metallic cover because of damaged insulation, the cover comes to the mains voltage and anyone who touches it gets a severe shock. The earth wire provides a low-resistance path for this leakage current to the earth, so the cover stays at the potential of the earth and the user does not get a severe electric shock; the large current in this path also blows the fuse and cuts off the supply.
    Step-by-step solution →

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