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CBSE Class 10 Science 2026 — Paper 31/5/3

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

32 of its 45 questions also appear in 31/5/1, 31/5/2 and other papers; 13 are only in this paper.

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Questions 1–9 · 1 mark each

  1. Q1 1 mark

    Also in 31/5/1 (Q3), 31/5/2 (Q4)

    Choose the equation of reaction that correctly represents anaerobic respiration in muscles :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/5/1 (Q6), 31/5/2 (Q5)

    Which of the following is a non-biodegradable pollutant ?
    1. (a)Paper
    2. (b)DDT
    3. (c)Wood
    4. (d)Vegetable peel
    Show answer
    (b) DDT
    Step-by-step solution →
  3. Q3 1 mark
    An ecosystem contains maximum number of :
    1. (a)Producers
    2. (b)Herbivores
    3. (c)Carnivores
    4. (d)Omnivores
    Show answer
    (a) Producers
    Step-by-step solution →
  4. Q4 1 mark

    Also in 31/5/1 (Q1), 31/5/2 (Q3)

    Identify the part that controls the closing and opening of the stomatal pore in leaves of plants. Select the correct option.
    1. (a)Stomata
    2. (b)Epidermal cells
    3. (c)Guard cells
    4. (d)Chloroplasts
    Show answer
    (c) Guard cells
    Step-by-step solution →
  5. Q5 1 mark
    Select the incorrect statement from the following :
    1. (a)Ozone is a molecule formed by three atoms of oxygen.
    2. (b)Ozone shields earth's surface from harmful infrared radiations.
    3. (c)CFC's are linked to decline of layer in our atmosphere.
    4. (d)Ozone at higher levels is a product of UV radiations acting on oxygen molecule.
    Show answer
    (b) Ozone shields earth's surface from harmful infrared radiations.
    Step-by-step solution →
  6. Q6 1 mark

    Also in 31/5/1 (Q4), 31/5/2 (Q1)

    In human beings, the implantation of fertilised egg takes place in which part of female reproductive system ?
    1. (a)Oviduct
    2. (b)Cervix
    3. (c)Uterus
    4. (d)Vagina
    Show answer
    (c) Uterus
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/5/1 (Q5), 31/5/2 (Q6)

    When a human egg is fertilized by a sperm having ‘Y’ chromosome, the zygote has the following combination of chromosomes :
    1. (a)44 + XX
    2. (b)22 + XX
    3. (c)44 + XY
    4. (d)22 + XY
    Show answer
    (c) 44 + XY
    Step-by-step solution →
  8. Q8 1 mark

    Also in 31/5/1 (Q8)

    Question No. 8 & 9 consists of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option from (a), (b), (c) and (d) given below :

    Assertion (A): Bacteria that can withstand heat have better chances of survival in a heat wave.

    Reason (R): Accumulation of variations in a species increases the chances of its survival in changing environment.

    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
    Question No. 8 & 9 consists of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option from (a), (b), (c) and (d) given below :

    Assertion (A): In case of iodine deficiency in our diet, there is a possibility that we might suffer from goitre.

    Reason (R): One of the symptoms of goitre is swelling of neck.

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

Questions 10–12 · 2 marks each

  1. Q10 2 marks

    Also in 31/5/1 (Q12), 31/5/2 (Q11)

    Briefly mention the steps in double-circulation through human heart.
    Show answer

    Blood passes twice through the heart: body to right atrium, right ventricle, lungs, left atrium, left ventricle and back to the body.

    Double circulation means that blood passes through the heart twice in one complete round of the body: (1) Deoxygenated blood from the body enters the right atrium through the vena cava; the right atrium contracts and passes it to the right ventricle. (2) The right ventricle pumps it through the pulmonary artery to the lungs, where it gives up and takes up . (3) The oxygenated blood returns through the pulmonary veins to the left atrium, which contracts and passes it to the left ventricle. (4) The left ventricle pumps it through the aorta to all parts of the body; there it gives up oxygen and returns to the right atrium, and the cycle repeats. Steps (2) and (3) form the pulmonary circulation (heart to lungs to heart) and steps (4) and (1) the systemic circulation (heart to body to heart). Valves stop the blood from flowing backwards.
    Step-by-step solution →
  2. Q11 2 marks
    Why the lungs always contain a residual volume of air ?
    Show answer

    Residual air keeps gas exchange going between breaths, giving sufficient time for oxygen to be absorbed and carbon dioxide released.

    The lungs never empty completely so that gaseous exchange never has to stop. Breathing is rhythmic, so fresh air reaches the alveoli only when we breathe in, but blood flows through the capillaries around the alveoli all the time. Because a residual volume of air always stays in the alveoli, oxygen keeps diffusing from this air into the blood and carbon dioxide keeps diffusing from the blood into it, even while we are breathing out and between one breath and the next. There is therefore sufficient time for oxygen to be absorbed and for carbon dioxide to be released. The air left behind also keeps the alveoli inflated, so the large exchange surface stays open instead of collapsing at the end of every expiration.
    Step-by-step solution →
  3. Q12(a) 2 marks

    Also in 31/5/1 (Q11(a)), 31/5/2 (Q10(a))

    Observe the given figure and identify the labelled parts P, Q, R and S :
    Message to brain Spinal cord (CNS) P Q R S
    Show answer

    P is the receptor, Q the sensory neuron, R the relay neuron and S the effector (arm muscle).

    P - Receptor: the heat and pain receptors in the skin of the hand, which detect the stimulus. Q - Sensory neuron: it carries the impulse from the receptor to the spinal cord. R - Relay neuron: the neuron inside the spinal cord that passes the impulse from the sensory neuron to the motor neuron. S - Effector: the muscle of the arm, which contracts and pulls the hand away.
    Step-by-step solution →
    OR
    Q12(b) 2 marks

    Also in 31/5/1 (Q11(b)), 31/5/2 (Q10(b))

    Which of the plant hormones are responsible for the following processes ?
    1. (i)Promote cell division
    2. (ii)Inhibition of growth
    3. (iii)Detection of light
    4. (iv)Wilting of leaves
    Show answer

    Cytokinin promotes cell division, abscisic acid inhibits growth and causes wilting, and auxin bends the shoot towards light.

    (i) Cytokinin - it promotes cell division. (ii) Abscisic acid - it is the growth inhibitor among the plant hormones. (iii) Auxin - it gathers on the shaded side of a shoot, makes those cells grow longer and bends the shoot towards the light. (iv) Abscisic acid - it closes the stomata under water stress, and wilting of leaves is among its effects.
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks

    Also in 31/5/1 (Q14), 31/5/2 (Q13)

    1. (a)Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags.
    2. (b)Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies ? What is this phenomenon known as ?
    Show answer

    Plastic bags persist for years, so use cloth, jute or paper bags; chemicals reach us through the food chain by biological magnification.

    (a) Harmful effect (any one): plastic bags are non-biodegradable, so they persist in the environment for years; they choke drains and sewers and cause water-logging, they stop water and air from entering the soil they cover, and animals that swallow them may die. Better alternatives: cloth or jute bags, which can be used again and again, and paper bags, which are biodegradable. (b) The chemicals are washed into the soil and water bodies; from the soil the paddy and other plants absorb them along with water and minerals, and in water bodies aquatic plants and animals take them up, so they enter the food chain. Being non-degradable they are not broken down or excreted, so they get accumulated at each trophic level, and human beings, who are at the top of the food chain, get the maximum concentration through food such as rice, vegetables and fish. This phenomenon is known as biological magnification.
    Step-by-step solution →
  2. Q14 3 marks
    1. (a)Show a cross between a pea plant having round & green seed with a pea plant having wrinkled and yellow seeds upto generation.
    2. (b)Also write down results of generation.
    Show answer

    is all round yellow (); gives round yellow : round green : wrinkled yellow : wrinkled green .

    (a) Round () is dominant over wrinkled () and yellow () over green (), so the parents are (round, green) and (wrinkled, yellow). Their only gametes are and , so the whole is and bears round, yellow seeds. Selfing the () gives the four gametes , , and from each side, and the Punnett square of holds combinations, row by row (gametes , , , along both sides): , , , ; , , , ; , , , ; , , , . (b) The generation gives four kinds of seed in the ratio — round yellow, round green, wrinkled yellow and wrinkled green out of every . The parental combinations round-green and wrinkled-yellow reappear, and the new combinations round-yellow and wrinkled-green appear as well, which shows that seed shape and seed colour are inherited independently of each other.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks

    Also in 31/5/1 (Q15), 31/5/2 (Q15)

    Kidneys help to regulate the volume of fluid and various metabolites waste products in the body. Normally, kidney filter about 180 L of fluid daily but the volume actually excreted out is only a litre or two a day. Patients with kidney failures can be saved by dialysis and kidney transplant.
    1. (a)Write the structure and function of Bowman’s capsule.[1]
    2. (b)Although kidneys filter a large amount (about 180 L daily) of fluids, still the excretion from the body is only about a litre or two. Why ?[1]
    3. (c)What is excretion ? Why is it necessary for any living organism ?[2]
    4. (c)OR : State two similarities between lungs and kidneys.[2]
    Show answer

    Bowman's capsule is a cup-shaped part holding the glomerulus that collects filtrate; about of filtrate is reabsorbed; excretion removes metabolic wastes.

    (a) Bowman’s capsule is the thin-walled, cup-shaped beginning of a nephron; it encloses the glomerulus, a cluster of very fine blood capillaries, and opens into the coiled tubule. Function: it collects the filtrate (water, glucose, amino acids, salts and urea) filtered out of the blood in the glomerulus and passes it into the tubule. (b) Because almost all of the filtrate is taken back. As it flows along the tubule, glucose, amino acids, salts and most of the water are selectively reabsorbed into the surrounding blood capillaries, about to L of the L, that is roughly , so only to L is left to be excreted as urine. (c) Excretion is the biological process by which the harmful waste products of metabolism are removed from the body. It is necessary because wastes such as urea and uric acid are made continuously in the cells and are poisonous if they collect in the body; removing them also keeps the water and salt content of the body fluids in balance. OR (c) Two similarities: (i) both are excretory organs that remove metabolic wastes from the blood, the lungs removing carbon dioxide and the kidneys nitrogenous wastes such as urea; (ii) in both, the exchange happens across a cluster of very thin-walled blood capillaries offering a large surface, around the alveoli in the lungs and in the glomerulus of each nephron. (Both are also paired organs with a rich blood supply.)
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks

    Also in 31/5/1 (Q16(b)), 31/5/2 (Q16(a))

    1. (i)Sugarcane does not produce seeds so name the process through which it will be able to reproduce.
    2. (ii)List any two advantages of this method.
    3. (iii)Besides sugarcane, give two more examples of plants that reproduce by this method.
    4. (iv)Why regeneration is not possible in all the types of animals ?
    Show answer

    Sugarcane reproduces by vegetative propagation, which keeps the parent's characters; complex animals cannot regenerate because their specialised cells cannot rebuild the whole body.

    (i) Vegetative propagation. Pieces of the sugarcane stem bearing nodes with buds are planted, and each bud grows into a new plant. (ii) Any two: the new plants are genetically similar to the parent, so the characteristics of a good variety are retained; they bear flowers and fruits earlier than plants grown from seeds; and the method allows plants that have lost the capacity to produce seeds (banana, orange, rose, jasmine) to be propagated. (iii) Rose and grapes (banana, jasmine, potato or Bryophyllum are equally acceptable). (iv) Regeneration is carried out by specialised cells that multiply and then change, in an organised sequence, into all the different cell types and tissues; only organisms that have such cells can regenerate. Simple animals such as Hydra and Planaria have them, so a cut piece can grow into a complete organism. Complex animals do not: their body cells have already become particular kinds of cells, organised into tissues, organs and organ systems that must lie at definite positions in the body, so a fragment cannot rebuild the entire organised body, and a whole individual cannot be regenerated.
    Step-by-step solution →
    OR
    Q16(b) 5 marks

    Also in 31/5/1 (Q16(a)), 31/5/2 (Q16(b))

    (i) In an angiospermic flower, fertilization is said to take place when male gametes carried in the pollen tube fuse with the female gamete, present in the embryo sac. This results in lot of changes in different parts of the flower. State the changes taking place in the following structures of flower post fertilization :
    1. (a)Zygote
    2. (b)Ovule
    3. (c)Ovary
    4. (d)Sepals (ii) Define germination.
    Show answer

    Zygote becomes embryo, ovule becomes seed, ovary becomes fruit and sepals fall off; germination turns the embryo into a seedling.

    (i)(a) Zygote: it divides repeatedly and develops into the embryo, which lies inside the ovule. (i)(b) Ovule: it develops a tough coat and is gradually converted into the seed, holding the embryo and its stored food. (i)(c) Ovary: it grows rapidly and ripens to form the fruit, whose wall encloses the seeds. (i)(d) Sepals: they usually shrivel and fall off, along with the petals, stamens, style and stigma; in some plants, such as brinjal, they stay attached to the fruit. (ii) Germination is the process in which the embryo inside a seed develops into a seedling under appropriate conditions of water, air (oxygen) and suitable temperature.
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark

    Also in 31/5/1 (Q19), 31/5/2 (Q18)

    Which of the following is an amphoteric oxide ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  2. Q18 1 mark

    Also in 31/5/1 (Q21), 31/5/2 (Q22), 31/8/3/SB (Q19)

    Which of the following will not undergo addition reaction ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (c)
    Step-by-step solution →
  3. Q19 1 mark
    Magnesium ribbon burns with a dazzling white flame and changes into a white powder as shown in the diagram given below : The powder is dissolved in water. Identify the chemical formula of the white powder and the correct change observed when the solution is tested with litmus paper.
    Tong Magnesium ribbon Burner Watch-glass Magnesium oxide
    1. (a), turns blue litmus into red.
    2. (b), turns red litmus blue.
    3. (c), turns red litmus blue.
    4. (d), turns blue litmus red.
    Show answer
    (b) , turns red litmus blue.
    Step-by-step solution →
  4. Q20 1 mark

    Also in 31/5/1 (Q18), 31/5/2 (Q17)

    Which of the following set of compounds does not belong to same homologous series ?
    1. (a) and
    2. (b) and
    3. (c) and
    4. (d) and
    Show answer
    (d) and
    Step-by-step solution →
  5. Q21 1 mark

    Also in 31/5/1 (Q22)

    Four solutions, namely fructose, ethanol, hydrochloric acid and sodium hydroxide filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :
    1. (a)ethanol and hydrochloric acid
    2. (b)fructose and ethanol
    3. (c)fructose and sodium hydroxide
    4. (d)hydrochloric acid and sodium hydroxide
    Show answer
    (d) hydrochloric acid and sodium hydroxide
    Step-by-step solution →
  6. Q22 1 mark

    Also in 31/5/1 (Q20), 31/5/2 (Q21)

    Study the following table and select the correct option :
    OptionSaltAcid usedBase usedNature of Salt
    (a)NaClHClNaOHBasic
    (b)Na₂CO₃H₂CO₃NaOHNeutral
    (c)Na₂SO₄H₂SO₄NaOHAcidic
    (d)CH₃COONaCH₃COOHNaOHBasic
    1. (a)Salt: ; Acid used: ; Base used: ; Nature of Salt: Basic
    2. (b)Salt: ; Acid used: ; Base used: ; Nature of Salt: Neutral
    3. (c)Salt: ; Acid used: ; Base used: ; Nature of Salt: Acidic
    4. (d)Salt: ; Acid used: ; Base used: ; Nature of Salt: Basic
    Show answer
    (d) Salt: ; Acid used: ; Base used: ; Nature of Salt: Basic
    Step-by-step solution →
  7. Q23 1 mark
    Galvanization is a process of coating iron articles with a thin layer of zinc to prevent iron from rusting. The iron is protected even if the zinc coating is scratched and iron is exposed. Which of the following is/are true about how zinc prevents the rusting of iron ? (P) A galvanised iron article does not undergo oxidation. (Q) The zinc coating prevents contact of iron with air. (R) Zinc provides continuous protection to iron from rusting.
    1. (a)Only (P)
    2. (b)Only (Q)
    3. (c)(Q) and (R)
    4. (d)(P) and (Q)
    Show answer
    (c) (Q) and (R)
    Step-by-step solution →
  8. Q24 1 mark

    Also in 31/5/1 (Q24), 31/5/2 (Q24)

    In the question two statements are given – one labelled as Assertion (A) and other labelled as Reason (R). Answer this question selecting the appropriate option from (a), (b), (c) and (d) given below :

    Assertion (A): Reaction of quick lime with water is an exothermic reaction.

    Reason (R): A large amount of heat is evolved on the reaction of quick lime and water.

    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
    Write the preparation of Baking soda. How does it help in making cakes soft and spongy ?
    Show answer

    Carbon dioxide passed into ammonia-saturated sodium chloride solution gives baking soda; on heating it releases carbon dioxide, which makes the cake soft and spongy.

    Preparation: baking soda is sodium hydrogencarbonate, . It is made by passing carbon dioxide through a cold concentrated solution of sodium chloride saturated with ammonia, when the sparingly soluble sodium hydrogencarbonate separates out: . Use in baking: baking soda is mixed with a mild edible acid such as tartaric acid to give baking powder, which is added to the cake batter. On heating in the oven the sodium hydrogencarbonate decomposes, , and the carbon dioxide given off is trapped in the thick batter. The bubbles raise the batter and, when the cake sets, leave behind the pores that make it soft and spongy. The tartaric acid neutralises the sodium carbonate formed, so the cake does not taste bitter.
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26 3 marks
    What happens when
    1. (i)potassium iodide solution is added to lead (II) nitrate solution ?
    2. (ii)zinc is added to copper (II) chloride solution ?
    3. (iii)hydrogen gas is passed over hot copper (II) oxide ? Write balanced chemical equations of the reactions involved in support of your answer.
    Show answer

    Yellow lead iodide precipitates; zinc displaces copper, fading the blue solution; hot copper(II) oxide is reduced to copper by hydrogen.

    (i) A bright yellow precipitate of lead iodide is formed and the mixture turns yellow; this is a double displacement, or precipitation, reaction: . (ii) Zinc, being more reactive than copper, displaces copper from the solution: the blue colour of the copper (II) chloride solution fades to the colourless solution of zinc chloride and a reddish-brown deposit of copper forms on the zinc: . (iii) The black copper (II) oxide is reduced to reddish-brown copper while the hydrogen is oxidised to water, which condenses at the cool end of the tube: .
    Step-by-step solution →
  2. Q27(a) 3 marks

    Also in 31/5/1 (Q27(a)), 31/5/2 (Q27(a))

    1. (a)Give the chemical name and formula of Plaster of Paris.
    2. (b)Write the chemical equation of its preparation.
    3. (c)Give any two uses of it.
    Show answer

    Plaster of Paris is calcium sulphate hemihydrate, made by heating gypsum at 373 K; it supports fractured bones and is used for toys.

    (a) Plaster of Paris is calcium sulphate hemihydrate (calcium sulphate half water), . (b) It is prepared by heating gypsum at K: . (c) Any two uses: doctors use it as plaster for supporting fractured bones in the right position; it is used for making toys, decorative materials and for making surfaces smooth.
    Step-by-step solution →
    OR
    Q27(b) 3 marks

    Also in 31/5/1 (Q27(b)), 31/5/2 (Q27(b))

    1. (a)Name the acid present in ant’s sting.
    2. (b)Give reason : (i) While diluting an acid, it is recommended that the acid should be added to water. (ii) Baking soda is used as an antacid.
    Show answer

    Ant stings contain methanoic acid; acid is added to water because dilution is exothermic; baking soda, a mild base, neutralises stomach acid.

    (a) Methanoic acid (formic acid), . (b)(i) The dilution of an acid is a highly exothermic process. If water is added to a concentrated acid, the small amount of water becomes so hot that it boils, the mixture splashes out and can cause burns, and the container may crack from the local heating. Adding the acid slowly to a large volume of water, with constant stirring, lets the water absorb the heat safely. (ii) Baking soda (sodium hydrogencarbonate) is a mild base. It neutralises the excess hydrochloric acid in the stomach and gives relief from acidity: .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks

    Also in 31/5/1 (Q28), 31/5/2 (Q28)

    Alcohol forms a homologous series with general formula and group as functional group. Ethanol is commonly called alcohol and is used in alcoholic drinks. It is good solvent, used in medicines, cough syrups, tonics etc.
    1. (a)Write structural formula and name of 4th member of alcohol homologous series.[1]
    2. (b)What happens when ethanol is heated with alkaline ? Write chemical equation involved.[1]
    3. (c)Write the chemical equation of reaction of ethanol with ethanoic acid in the presence of concentrated . Write the name of this reaction.[2]
    4. (c)OR : What happens when ethanol is heated with excess concentrated sulphuric acid at K ? Write chemical equation involved. What is the role of concentrated sulphuric acid in this reaction ?[2]
    Show answer

    The 4th alcohol is butanol, ; ethanol is oxidised to ethanoic acid; ethanol and ethanoic acid give an ester by esterification.

    (a) The 4th member is butanol (butan-1-ol), ; its structural formula is , drawn out in full as (b) Ethanol is oxidised to ethanoic acid (the purple colour of the permanganate fades): . (c) ; the reaction is esterification and the product, ethyl ethanoate, is a sweet-smelling ester. OR (c) Ethanol is dehydrated to ethene: ; the concentrated sulphuric acid acts as a dehydrating agent.
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks

    Also in 31/5/1 (Q29(a)), 31/5/2 (Q29(a))

    1. (i)Give reasons for the following : (I) Ionic compound have generally high melting points and boiling points. (II) Solder, an alloy of lead and tin, is used for welding electrical wires. (III) Carbon cannot reduce the oxides of Na or Mg.
    2. (ii)The reaction of compound ‘X’ with aluminium is used to join railway tracks : (I) Identify the compound ‘X’. (II) Name the reaction. (III) Write the balanced chemical equation of the reaction of compound ‘X’ with aluminium.
    Show answer

    Strong ionic attractions give high melting points; solder melts easily; carbon cannot reduce Na or Mg oxides; X is in the thermit reaction.

    (i)(I) In an ionic compound the oppositely charged ions are held together by strong electrostatic forces of attraction, and a considerable amount of energy is needed to overcome them; hence the high melting and boiling points. (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, being metallic, conducts electricity. (III) Sodium and magnesium lie above carbon in the reactivity series and have a greater affinity for oxygen than carbon has, so carbon cannot remove the oxygen from their oxides; such metals are obtained by electrolytic reduction. (ii)(I) ‘X’ is iron(III) oxide, . (II) The reaction is the thermit reaction. (III)
    Step-by-step solution →
    OR
    Q29(b) 5 marks

    Also in 31/5/1 (Q29(b)), 31/5/2 (Q29(b))

    1. (i)Write the balanced chemical equations when : (I) A mixture of and is heated. (II) is heated in the presence of oxygen.
    2. (ii)Give reasons for the following : (I) The wires carrying current in homes have a coating of PVC. (II) To make hot water tanks, copper is used and not steel.
    3. (iii)Show the formation of ionic compound with electron dot structure. [Atomic number : , ]
    Show answer

    Self-reduction gives copper and roasting gives ; PVC insulates, copper resists steam, and forms when Ca transfers two electrons to O.

    (i)(I) (self-reduction). (II) (roasting). (ii)(I) PVC is an electrical insulator; its coating on the copper wire keeps the current inside the wire and so prevents electric shocks and short circuits. (II) Copper does not react with water, hot water or steam, whereas the iron in steel reacts with steam, , and also rusts, so a steel tank would corrode; copper is also a good conductor of heat. (iii) Calcium () transfers its two valence electrons to oxygen (), giving () and (), which are held together by an ionic bond:
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark

    Also in 31/5/1 (Q30), 31/5/2 (Q31)

    Rays from the sun converge at a point cm behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is :
    1. (a) cm
    2. (b) cm
    3. (c) cm
    4. (d)More than cm
    Show answer
    (a) cm
    Step-by-step solution →
  2. Q31 1 mark

    Also in 31/5/1 (Q31), 31/5/2 (Q30)

    To restore clear vision in persons whose size of the eye ball has reduced, he/she is suggested to use suitable
    1. (a)Converging lens
    2. (b)Diverging lens
    3. (c)Bifocal lens
    4. (d)Cylindrical lens
    Show answer
    (a) Converging lens
    Step-by-step solution →
  3. Q32 1 mark

    Also in 31/5/1 (Q32), 31/5/2 (Q32)

    For question number 32, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below :

    Assertion (A): The needle of a magnetic compass kept in strong external magnetic field, always aligns itself in north-south direction on the earth.

    Reason (R): Behaviour of the needle of a compass is same as that of a freely suspended bar magnet.

    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
    (d) Assertion (A) is false, but Reason (R) is true.
    Step-by-step solution →

Questions 33–34 · 2 marks each

  1. Q33 2 marks
    When an incident ray of light enters in a medium 'X' from medium 'Y', it bends away from the normal. Comment about the following :
    1. (a)Speed of light in medium 'X' with respect to the speed of light in medium of 'Y'.
    2. (b)Optical density of medium 'X' with respect to the optical density of medium 'Y'. Give reason for your answer in each case.
    Show answer

    Light travels faster in X than in Y, so X is optically rarer than Y.

    (a) The speed of light in medium 'X' is greater than the speed of light in medium 'Y'. A ray turns away from the normal only when it passes into a medium in which light travels faster, and makes the faster medium the one with the smaller refractive index. (b) Medium 'X' is optically rarer than medium 'Y'. From with we get , and of two media the one with the smaller refractive index is the optically rarer.
    Step-by-step solution →
  2. Q34(a) 2 marks

    Also in 31/5/1 (Q34(a)), 31/5/2 (Q34(a))

    1. (i)How does the change in curvature of the eye lens helps us in the process of seeing the nearby objects clearly ?
    2. (ii)State the range of the power of accommodation of a normal human eye.
    Show answer

    Contracting ciliary muscles thicken the lens, shortening its focal length for near objects; normal range is about 25 cm to infinity.

    (i) To see a nearby object clearly the ciliary muscles contract, which increases the curvature of the eye lens so that it becomes thicker. A more curved lens has a shorter focal length (greater power), so it converges the steeply diverging light coming from the nearby object enough to form a sharp image on the retina, whose distance from the lens cannot change. This adjustment of focal length is called accommodation; for a distant object the muscles relax, the lens thins and its focal length increases. (ii) A normal human eye can see objects clearly from its near point, about cm, to its far point at infinity; over this range the power of its lens changes by about D.
    Step-by-step solution →
    OR
    Q34(b) 2 marks

    Also in 31/5/1 (Q34(b)), 31/5/2 (Q34(b))

    Draw a ray diagram to show the correction of eye defect of an old man who can not see an object placed closer than 1 m from his eye, clearly.
    Show answer

    Presbyopia, corrected by a convex lens of power D (focal length cm).

    The old man's near point has receded to m, so he suffers from presbyopia: with age the ciliary muscles weaken and the eye lens loses its flexibility, so the near point recedes. For near vision it behaves like long-sightedness (hypermetropia) - light from a nearby object would be focused behind the retina. It is corrected with spectacles carrying a convex (converging) lens: to read at the normal cm, per cm, so cm cm and D. Ray diagram: the object stands at ( cm); the convex lens in front of the eye bends the rays from so that they leave it diverging as if from ( m, his near point - shown by dashed backward extensions), and the eye lens then focuses them on the retina. Arrows on every ray show the direction of light.
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks

    Also in 31/5/1 (Q35), 31/5/2 (Q37)

    1. (a)Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation.
    2. (b)When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change ? Explain.
    Show answer

    The angle of deviation remains the same, because the reversed ray retraces its path and depends only on .

    (a) A ray PE falls on face AB of the prism at E and, bending towards the normal , travels through the glass along EF; at F on face AC it bends away from the normal and emerges along FS. Marked on the diagram: the angle of refraction , between EF and the normal at E, and the angle of deviation , between the incident ray PE produced forward and the emergent ray FS produced backward (with , and the angle of the prism shown as well). (b) The angle of deviation does not change - it remains the same. By the reversibility of light the reversed ray retraces the original path, so its angle of incidence is the old angle of emergence and its angle of emergence the old angle of incidence; since depends only on the sum , interchanging the two leaves the deviation unchanged.
    Step-by-step solution →
  2. Q36 3 marks
    An object of height 6 cm is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine :
    1. (a)The distance of image from the optical centre.
    2. (b)The height of the image formed.
    Show answer

    The image is 10 cm from the optical centre, on the object's side, and 2 cm tall (virtual, erect, diminished).

    (a) cm, so the image is formed cm from the optical centre, on the same side of the lens as the object. (b) cm, so the image is cm tall. It is virtual, erect and diminished.
    Step-by-step solution →
  3. Q37 3 marks

    Also in 31/5/1 (Q37), 31/5/2 (Q35)

    1. (a)Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON ?
    2. (b)How to connect three resistors each of resistance , so that the equivalent resistance of the combination is ? Draw diagram of the combination and justify your answer.
    Show answer

    The heater's large current lowers the voltage across the bulb; two resistors in parallel plus one in series give .

    (a) A bulb and a heater in a house are joined in parallel across the supply. The heater has a low resistance, so when it is switched on it draws a large current and the total current drawn from the mains increases greatly. This larger current flows through the supply wires, which have some resistance , so a larger potential difference is used up in them and the potential difference left across the bulb decreases. As a result the current through the bulb decreases, its power falls, and the bulb glows dim. (b) Connect two of the resistors in parallel and join this combination in series with the third resistor. Justification: for the parallel pair , so ; in series with the third resistor, .
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks

    Also in 31/5/1 (Q38), 31/5/2 (Q38)

    Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire. Shweta put nichrome wire of length ‘’ in the circuit and after plugging the key, noted current in the ammeter. Ayesha put nichrome wire of same thickness but twice the length i.e. ‘’ in the circuit and after plugging the key, noted current in the ammeter. Samridhi took copper wire of length ‘’ and same thickness in the circuit and after plugging the key, noted current in the ammeter.
    1. (a)If the ammeter reading is ampere with nichrome wire of length ‘’, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?
    2. (b)What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ‘’ the same ?
    3. (c)Define ‘resistivity’. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.
    4. (c)OR : Give reason : (i) Tungsten is used almost exclusively for making the filament of electric lamps. (ii) Conductors of bread-toasters are made of an alloy rather than a pure metal.
    Show answer

    Current halves to for double length and doubles to for double area; resistivity is , in ohm metre.

    (a) Doubling the length doubles the resistance (), so with the same cell the current is halved: the ammeter reads ampere. (b) Doubling the area of cross-section halves the resistance, so the ammeter reading is doubled, to ampere. (c) Resistivity is the resistance of a conductor of the material having unit length and unit area of cross-section, ; its SI unit is the ohm metre ( m). The resistivity of an alloy is generally much higher than that of its constituent metals - nichrome, for instance, has about m against nickel's m - and alloys do not oxidise readily at high temperatures. OR (c) (i) Tungsten has a very high melting point (about C) and a high resistivity, and it can be drawn into a fine, strong wire, so its filament can be kept white hot and glow without melting. (ii) An alloy has a much higher resistivity than a pure metal, so for the same current () the element gives out far more heat than the connecting wires, and an alloy does not oxidise (burn) readily at high temperature, so the heating conductor lasts.
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)State the rule which gives the direction of force acting on a current carrying conductor placed in a uniform magnetic field.
    2. (ii)Name any two devices which work on the basis of an interaction between magnetic field and current carrying conductor.
    3. (iii)Observe the given diagrams : Comment on the magnitude of force on electron in both the cases and give reason for your answer.
    Magnetic Field e Movement of electron (I) Magnetic Field e Movement of electron (II)
    Show answer

    The force on the electron is maximum in case (I) and zero in case (II); Fleming's left-hand rule gives its direction.

    (i) Fleming's left-hand rule. Stretch the thumb, the forefinger and the middle finger of the left hand so that they are mutually perpendicular; if the forefinger points along the magnetic field and the middle finger along the current, the thumb points in the direction of the force on the conductor. (ii) Electric motor and loudspeaker. (A moving-coil galvanometer or ammeter is an equally good answer.) (iii) The force is maximum in case (I) and zero in case (II). Since , in case (I) the electron moves at right angles to the field, and , giving ; in case (II) the electron moves along the field, and , so no magnetic force acts on it.
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)List three possible reasons of short-circuiting in an electric circuit.
    2. (ii)In case of overload, will the fuse protect to given electric circuit from damage ? Justify your answer.
    3. (iii)For an electric heater rated as 220 V, 2200 W, what should be the minimum rating of fuse used with it ?
    Electric heater Fuse Neutral wire Live wire 220 V AC supply
    Show answer

    No, the fuse sits in the neutral wire; the heater draws 10 A, so its fuse rating should be slightly more than 10 A.

    (i) Three possible reasons for short-circuiting: (1) direct contact between the live wire and the neutral wire, for instance through a fault inside an appliance or a loose joint; (2) damaged or worn-out insulation on the wires, which lets the bare live and neutral wires touch; (3) overloading — too many appliances drawing current through one circuit overheats the wires, which can melt their insulation and let the live and neutral wires touch. (ii) No. In the circuit shown the fuse is connected in the neutral wire, but a fuse must be connected in series with the live wire. Even if an overload melts this fuse and stops the current, the heater and its wiring stay joined to the live wire at V, so the circuit is not made safe, and a leakage from the live wire to earth would not blow the fuse at all. (iii) A. The fuse must carry this A in normal use without melting, so its minimum rating should be slightly more than A.
    Step-by-step solution →

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