Quest4Learn
Sign in Start free

CBSE Class 10 Science 2025 — Paper 31/1/1

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

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

Take this paper as a timed mock

Free with an account: the board's time limit, marking at the end, and the answer to every question.

Sign up free Log in

Questions 1–20 · 1 mark each

  1. Q1 1 mark

    Also in 31/1/2 (Q5), 31/1/3 (Q7)

    Electrolysis of water is a decomposition reaction. The mass ratio () of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/1/2 (Q7), 31/1/3 (Q6)

    The products formed when Aluminium and Magnesium are burnt in the presence of air respectively are :
    1. (a) and
    2. (b) and
    3. (c) and
    4. (d) and
    Show answer
    (b) and
    Step-by-step solution →
  3. Q3 1 mark
    The following table shows the pH values of four solutions A, B, C and D on a pH scale : The solutions A, B, C and D respectively are of a
    1 2 3 4 5 6 7 8 9 10 11 12 13 14 B C D A
    1. (a)Strong acid, weak acid, neutral, strong base
    2. (b)Weak acid, neutral, weak base, strong base
    3. (c)Weak acid, neutral, strong base, weak base
    4. (d)Weak acid, neutral, strong base, strong acid
    Show answer
    (d) Weak acid, neutral, strong base, strong acid
    Step-by-step solution →
  4. Q4 1 mark

    Also in 31/1/2 (Q6), 31/1/3 (Q4)

    Consider the following reactions :
    1. (i)Dilute hydrochloric acid reacts with sodium hydroxide.
    2. (ii)Magnesium oxide reacts with dilute hydrochloric acid.
    3. (iii)Carbon dioxide reacts with sodium hydroxide. It is found that in each case :
    1. (a)Salt and water is formed.
    2. (b)Neutral salts are formed.
    3. (c)Hydrogen gas is formed.
    4. (d)Acidic salts are formed.
    Show answer
    (a) Salt and water is formed.
    Step-by-step solution →
  5. Q5 1 mark

    Also in 31/1/2 (Q4), 31/1/3 (Q3)

    Reaction between two elements A and B, forms a compound C. A loses electrons and B gains electrons. Which one of the following properties will not be shown by compound C ?
    1. (a)It has high melting point.
    2. (b)It is highly soluble in water.
    3. (c)It has weak electrostatic forces of attraction between its oppositely charged ions.
    4. (d)It conducts electricity in its molten state or aqueous solution.
    Show answer
    (c) It has weak electrostatic forces of attraction between its oppositely charged ions.
    Step-by-step solution →
  6. Q6 1 mark

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

    The metals obtained from their molten chlorides by the process of electrolytic reduction are :
    1. (a)Gold and silver
    2. (b)Calcium and magnesium
    3. (c)Aluminium and silver
    4. (d)Sodium and iron
    Show answer
    (b) Calcium and magnesium
    Step-by-step solution →
  7. Q7 1 mark

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

    The formation of magnesium oxide is correctly shown in option :
    (A) Mg O × × × × × × Mg²⁺ [ O × × × × × × ²⁻ ] (B) Mg O × × × × × × × Mg⁺ [ O × × × × × × × ⁻ ] (C) Mg + O × × × × × × × O × × × × × × × Mg²⁺ [ O × × × × × × × ⁻ ] ₂ (D) 2Mg × O [ Mg²⁺ ] ₂ [ O ²⁻ ]
    1. (a)One atom transfers both of its outer electrons to a single atom, giving and one oxide ion with a complete octet, written .
    2. (b)One atom transfers a single electron to one atom, giving and one ion.
    3. (c)One atom transfers one electron to each of two atoms, giving and two ions, written .
    4. (d)Two atoms transfer electrons to a single atom, giving and one ion.
    Show answer
    (a) One atom transfers both of its outer electrons to a single atom, giving and one oxide ion with a complete octet, written .
    Step-by-step solution →
  8. Q8 1 mark

    Also in 31/1/2 (Q9), 31/1/3 (Q12)

    Secretion of less saliva in mouth will effect the conversion of :
    1. (a)proteins into amino acids
    2. (b)fats into fatty acids and glycerol
    3. (c)starch into simple sugars
    4. (d)sugars into alcohol
    Show answer
    (c) starch into simple sugars
    Step-by-step solution →
  9. Q9 1 mark

    Also in 31/1/2 (Q8), 31/1/3 (Q11)

    The plant hormone whose concentration stimulates the cells to grow longer on the side of the shoot which is away from light is :
    1. (a)Cytokinins
    2. (b)Gibberellins
    3. (c)Adrenaline
    4. (d)Auxins
    Show answer
    (d) Auxins
    Step-by-step solution →
  10. Q10 1 mark

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

    The correct/true statement(s) for a bisexual flower is/are :
    1. (i)They possess both stamen and pistil.
    2. (ii)They possess either stamen or pistil.
    3. (iii)They exhibit either self-pollination or cross-pollination.
    4. (iv)They cannot produce fruits on their own.
    1. (a)(i) only
    2. (b)(iv) only
    3. (c)(i) and (iii)
    4. (d)(i) and (iv)
    Show answer
    (c) (i) and (iii)
    Step-by-step solution →
  11. Q11 1 mark

    Also in 31/1/2 (Q10), 31/1/3 (Q9)

    If pea plants with round and green seeds () are crossed with pea plants having wrinkled and yellow seeds (), the seeds developed by the plants of generation will be :
    1. (a) round and green
    2. (b) wrinkled and green
    3. (c) round and yellow
    4. (d) wrinkled and yellow
    Show answer
    (c) round and yellow
    Step-by-step solution →
  12. Q12 1 mark

    Also in 31/1/2 (Q12), 31/1/3 (Q8)

    The breakdown of glucose has taken the following pathway : The sites ‘a’ and ‘b’ respectively are :
    1. (a)Mitochondria and Oxygen deficient muscle cells
    2. (b)Cytoplasm and Oxygen rich muscle cells
    3. (c)Cytoplasm and Yeast cells
    4. (d)Cytoplasm and Oxygen deficient muscle cells
    Show answer
    (d) Cytoplasm and Oxygen deficient muscle cells
    Step-by-step solution →
  13. Q13 1 mark

    Also in 31/1/2 (Q14), 31/1/3 (Q16)

    Mirror ‘X’ is used to concentrate sunlight in solar furnace and Mirror ‘Y’ is fitted on the side of the vehicle to see the traffic behind the driver. Which of the following statements are true for the two mirrors ?
    1. (i)The image formed by mirror ‘X’ is real, diminished and at its focus.
    2. (ii)The image formed by mirror ‘Y’ is virtual, diminished and erect.
    3. (iii)The image formed by mirror ‘X’ is virtual, diminished and erect.
    4. (iv)The image formed by mirror ‘Y’ is real, diminished and at its focus.
    1. (a)(i) and (ii)
    2. (b)(ii) and (iii)
    3. (c)(iii) and (iv)
    4. (d)(i) and (iv)
    Show answer
    (a) (i) and (ii)
    Step-by-step solution →
  14. Q14 1 mark
    An old person is suffering from an eye defect caused by weakening of ciliary muscles and diminishing flexibility of the eye lens. If the defect of vision is ‘a’ which can be corrected by lens ‘b’, then ‘a’ and ‘b’ respectively are :
    1. (a)hypermetropia and convex lens
    2. (b)presbyopia and bifocal lens
    3. (c)myopia and concave lens
    4. (d)myopia and bifocal lens
    Show answer
    (b) presbyopia and bifocal lens
    Step-by-step solution →
  15. Q15 1 mark

    Also in 31/1/2 (Q16), 31/1/3 (Q14)

    Which of the following groups do not constitute a food chain ?
    1. (i)Wolf, rabbit, grass, lion
    2. (ii)Plankton, man, grasshopper, fish
    3. (iii)Hawk, grass, snake, grasshopper, frog
    4. (iv)Grass, snake, wolf, tiger
    1. (a)(i) and (iv)
    2. (b)(i) and (iii)
    3. (c)(ii) and (iii)
    4. (d)(ii) and (iv)
    Show answer
    (d) (ii) and (iv)
    Step-by-step solution →
  16. Q16 1 mark

    Also in 31/1/2 (Q15), 31/1/3 (Q13)

    The percentage of solar energy which is not converted into food energy by the leaves of green plants in a terrestrial ecosystem is about :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  17. Q17 1 mark

    Also in 31/1/2 (Q19), 31/1/3 (Q20)

    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): Decomposition reactions are generally endothermic reactions.

    Reason (R): Decomposition of organic matter into compost is an exothermic process.

    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 →
  18. Q18 1 mark

    Also in 31/1/2 (Q17), 31/1/3 (Q19)

    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): A human child bears all the basic features of human beings.

    Reason (R): It looks exactly like its parents, showing very little variations.

    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 →
  19. Q19 1 mark

    Also in 31/1/2 (Q20), 31/1/3 (Q18)

    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): No two magnetic field lines are found to cross each other.

    Reason (R): The compass needle cannot point towards two directions at the point of intersection of two magnetic field lines.

    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 →
  20. Q20 1 mark

    Also in 31/1/2 (Q18), 31/1/3 (Q17)

    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 amount of ozone in the atmosphere began to drop sharply in the 1980s.

    Reason (R): The oxygen atoms combine with molecular oxygen to form ozone.

    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 21–26 · 2 marks each

  1. Q21 2 marks

    Also in 31/1/3 (Q25)

    A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.
    dilute sulphuric acid Zn granules
    Show answer

    A gas (hydrogen) bubbles off and the flask turns warm, showing that a chemical change has taken place.

    Observation 1: A colourless, odourless gas is given off. Bubbles rise steadily from the surface of the zinc granules and escape through the glass tube, and the gas burns with a pop when a lighted splint is brought to the mouth of the tube, showing it is hydrogen. Observation 2: The flask becomes warm to the touch, so heat is being given out and the reaction is exothermic. Both show that new substances have been formed: . (The zinc granules also gradually shrink and dissolve away, which is an acceptable third observation.)
    Step-by-step solution →
  2. Q22 2 marks

    Also in 31/1/2 (Q25), 31/1/3 (Q23)

    Draw labelled diagrams to show different stages of budding in Hydra.
    Show answer

    Budding in Hydra is shown in four stages: a bud forms, grows, develops mouth and tentacles, then detaches as a new Hydra.

    Budding in Hydra is shown as a sequence of four labelled drawings. Stage 1: A small bud appears as a bulge on one side of the parent's body wall, formed by repeated cell division at that site. Stage 2: The bud enlarges while remaining attached to the parent. Stage 3: The bud develops its own mouth and tentacles and becomes a miniature Hydra. Stage 4: The fully formed bud detaches from the parent and grows into a new, independent Hydra; the parent is unharmed and can bud again. Labels required: parent Hydra, bud, tentacles, mouth, basal disc and new (daughter) Hydra.
    Step-by-step solution →
  3. Q23(a) 2 marks

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

    Besides minimising the loss of blood, why is it essential to plug any leak in a blood vessel? Name the component of blood which helps in this process and state how this component perform this function.
    Show answer

    Plugging a leak keeps the pressure of the circulation; platelets stick at the cut and start clotting, and fibrin threads seal it.

    The blood inside our vessels is under pressure, and it is that pressure which drives blood to every tissue. If a leak is not plugged, the pressure in the system falls and the pumping of blood by the heart is no longer efficient, so the organs stop receiving enough blood. Plugging the leak therefore preserves the pressure of the circulation, not just its volume. The component of blood responsible is the platelet cell (thrombocyte). Platelets circulate all over the body. When a vessel is injured they reach the site, stick to the cut edges and pile up to form a temporary plug, and they set off the clotting process in which soluble fibrinogen of the plasma is converted into insoluble threads of fibrin. The fibrin mesh traps blood cells and forms a clot that seals the leak.
    Step-by-step solution →
    OR
    Q23(b) 2 marks

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

    1. (i)The transport system in plants is relatively slower than in animals. Give reasons.
    2. (ii)State the role of phloem in the transport of materials in plants.
    Show answer

    Plants have no pump and low energy needs, so transport is slow; phloem translocates sugars from leaves to other parts, upwards and downwards.

    (i) Plants have no pump. An animal's heart drives blood round a closed circuit under high pressure, whereas in a plant water rises only because evaporation from the leaves creates a transpiration pull, and food moves only because of osmotic pressure differences set up in the phloem; neither is driven by an organ. In addition, plants do not move about, so their energy needs are low, and a large part of a plant body is made of dead cells (xylem, wood and bark) which need nothing at all. A slow transport system is therefore sufficient for a plant. (ii) Phloem carries the products of photosynthesis - mainly soluble sugars such as sucrose, together with amino acids and other substances - from the leaves, where they are made, to the roots, growing buds, fruits and seeds where they are used or stored. This transport, called translocation, is an active process: material is loaded into the sieve tubes using energy from ATP, water then enters by osmosis and the resulting pressure moves the material to tissues at lower pressure. Because of this, phloem can carry material both upwards and downwards, unlike the xylem.
    Step-by-step solution →
  4. Q24 2 marks
    An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm. Use lens formula to find the position of the image formed in this case.
    Show answer

    cm: the image is 20 cm from the lens on the same side as the object.

    , so cm. The image is formed cm from the optical centre of the lens, on the same side as the object. The negative sign shows it is a virtual image; since , it is also erect and one-third the size of the object.
    Step-by-step solution →
  5. Q25(a) 2 marks
    A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.
    Show answer

    Each part has resistance ; the three in parallel give a total resistance of .

    Each part has resistance , because cutting changes only the length and at constant material and cross-section. In parallel, , so . The total resistance of the combination is , that is one-ninth of the resistance of the original wire.
    Step-by-step solution →
    OR
    Q25(b) 2 marks
    Define electric power. When do we say that the power consumed in an electric circuit is 1 watt?
    Show answer

    Electric power is the rate of consumption of electric energy; it is 1 watt when 1 ampere flows under 1 volt.

    Electric power is the rate at which electric energy is consumed or dissipated in an electric circuit, that is the electric work done per unit time: . Its SI unit is the watt (W). The power consumed in a circuit is said to be 1 watt when a current of 1 ampere flows through it under a potential difference of 1 volt: . Equivalently, the power is 1 watt when 1 joule of electrical energy is consumed every second, .
    Step-by-step solution →
  6. Q26 2 marks

    Also in 31/1/2 (Q21)

    “Excessive use of chemicals and pesticides in agriculture adversely effect the environment.” Justify this statement.
    Show answer

    Chemicals wash into soil and water, magnify along food chains to harm humans, and kill soil micro-organisms, so the statement is justified.

    Pesticides and chemical fertilisers sprayed on a field are washed by rain into the soil and into nearby water bodies. From the soil they are absorbed by plants along with water and minerals, and in water they are taken up by aquatic plants and animals, so they enter the food chain. These substances are non-biodegradable: they are neither broken down nor excreted. An animal keeps all of the chemical contained in the food it eats while building only a small part of that food into its own body, so the concentration of the chemical increases at every successive trophic level. This progressive increase is called biological magnification, and because human beings occupy the top level of the food chain, the maximum concentration accumulates in our bodies and causes serious health hazards. The same chemicals also kill useful soil micro-organisms and earthworms, so decomposition stops and soil fertility falls, and the run-off pollutes ponds and rivers and kills fish and other non-target organisms such as pollinators. The excessive use of these chemicals therefore damages the environment, which justifies the statement.
    Step-by-step solution →

Questions 27–33 · 3 marks each

  1. Q27 3 marks

    Also in 31/1/2 (Q31), 31/1/3 (Q33)

    1. (a)“Displacement reactions also play a key role in extracting metals in the middle of the reactivity series.” Justify this statement with two examples.
    2. (b)Why can metals high up in the reactivity series not be obtained by reduction of their oxides by carbon ?
    Show answer

    Aluminium displaces middle-of-series metals such as iron and manganese from their oxides; carbon cannot reduce the oxides of highly reactive metals.

    (a) Metals of medium reactivity (, , , ) are freed from their oxides by a **more** reactive metal, which displaces them; these displacement reactions are highly exothermic. Examples: (the thermit reaction, used to weld broken rails) and . (b) Metals high up in the series (, , , , ) have a far greater affinity for oxygen than carbon has, so their oxides are too stable for carbon to reduce — these metals are themselves stronger reducing agents than carbon. They are therefore obtained by electrolytic reduction of their molten chlorides or oxides.
    Step-by-step solution →
  2. Q28(a) 3 marks

    Also in 31/1/2 (Q30(a)), 31/1/3 (Q32(a))

    With the help of an activity, explain the conditions under which iron articles get rusted.
    Show answer

    Iron rusts only when both air and water are present: only the nail in the tube with air and water rusts.

    Rusting of iron needs **both** air (oxygen) and water (moisture). In the activity, clean iron nails are kept in three corked test tubes: A contains ordinary water with air above it; B contains boiled distilled water sealed under a layer of oil (water but no air); C contains anhydrous calcium chloride (air but no moisture). After a few days only the nail in tube A is covered with rust, while those in B and C stay shiny. Hence iron articles rust only when air and water are both present: (rust).
    Step-by-step solution →
    OR
    Q28(b) 3 marks

    Also in 31/1/2 (Q30(b)), 31/1/3 (Q32(b))

    1. (i)Name two metals which react violently with cold water. List any three observations which a student notes when these metal are dropped in a beaker containing water.
    2. (ii)Write a test to identify the gas evolved (if any) during the reaction of these metals with water.
    Show answer

    Potassium and sodium react violently with cold water, giving hydrogen, which burns with a pop sound near a burning splinter.

    (i) Potassium () and sodium () react violently with cold water. Three observations: (1) the metal floats on the water and darts about rapidly on the surface with a hissing sound; (2) there is brisk effervescence — bubbles of a colourless gas (hydrogen) are given off; (3) so much heat is evolved that the hydrogen catches fire (with a lilac flame over potassium; sodium also melts into a shiny silvery ball); the liquid left behind turns red litmus blue. . (ii) The gas evolved is hydrogen. Collect it in a test tube and bring a burning splinter to the mouth of the tube: the gas burns with a pale blue flame and a characteristic 'pop' sound, which confirms hydrogen.
    Step-by-step solution →
  3. Q29 3 marks
    Plants have neither a nervous system nor muscles, even then they respond to stimuli. For example, the leaves of chhui-mui (touch-me-not) plant when touched begin to fold up and droop.
    1. (a)How is the information communicated in “touch-me-not” plants ?
    2. (b)What enables the plant cells to bring out the observable response ?
    3. (c)Differentiate the movement mentioned above from the movement of tendrils in a pea plant.
    Show answer

    The signal passes cell to cell and leaflet-base cells lose water and shrink; this nastic movement is independent of growth, unlike tendril movement.

    (a) Plants have no nervous system, so the information that a leaf has been touched is passed on from cell to cell as an electrical–chemical signal (an electrical impulse together with chemical signals) which travels from the point of touch to the base of the leaflets. (b) Plant cells change shape by changing the amount of water in them. Cells at the base of the leaflets pump ions out; water follows and leaves those cells, so they lose water, shrink and lose their turgidity while the cells on the other side swell. This change in cell shape folds the leaflets and makes the leaf droop — no muscle cells are involved. (c) The touch-me-not movement is a nastic movement: it is independent of growth, is caused by a reversible change in the water content of cells, is very fast and reversible, and its direction is not decided by the direction of the stimulus. The movement of a pea tendril is a tropic (thigmotropic) movement: it is a growth movement caused by cells on the side away from the support growing longer than those touching it, is slow, is permanent, and is directional — the tendril grows towards and coils around the support.
    Step-by-step solution →
  4. Q30 3 marks
    1. (a)What are chromosomes ?
    2. (b)Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms ?
    Show answer

    Chromosomes carry the genes; meiosis halves the number in gametes and fertilisation restores it, so the DNA content of a species stays constant.

    (a) Chromosomes are thread-like structures present in the nucleus of a cell. They are made of DNA and protein and carry the genes, the units of inheritance that pass characters from parents to offspring; each species has a fixed number of them (46, that is 23 pairs, in human beings). (b) In sexual reproduction the progeny gets genetic material from both parents, so if each parent gave its full set the DNA content would double every generation (). This is prevented because the germ cells (gametes) are formed by meiosis, in which the chromosome number is **halved**: each gamete carries only one chromosome of each pair ( in human beings). When a male gamete fuses with a female gamete at fertilisation, the two haploid sets combine and the zygote regains the full diploid number (). Halving in the gametes and doubling at fertilisation therefore keep the DNA content of the species constant from one generation to the next.
    Step-by-step solution →
  5. Q31 3 marks

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

    Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed
    1. (i)at infinity and
    2. (ii)between infinity and pole P of the mirror.
    Show answer

    A convex mirror gives a virtual, erect, diminished image: at F for an object at infinity, and between P and F otherwise.

    (i) Object at infinity: the parallel beam is reflected so that the rays appear to diverge from the principal focus, so the image is formed **at** , behind the mirror. It is virtual, erect and highly diminished (point-sized). (ii) Object between infinity and the pole : the image is formed between and , behind the mirror. It is virtual, erect and diminished. Both results follow from the mirror formula, which gives (always positive and less than ) and (always positive and less than ), so a convex mirror always forms a virtual, erect, diminished image between and .
    Step-by-step solution →
  6. Q32 3 marks

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

    Consider the following electric circuit : Calculate the values of the following :
    1. (a)The total resistance of the circuit
    2. (b)The total current drawn from the source
    3. (c)Potential difference across the parallel combination of and resistors
    15 V 10 Ω 15 Ω A + − K 60 Ω 40 Ω
    Show answer

    Total resistance is , the current is A, and the and parallel pair has V across it.

    (a) Total resistance ; (b) total current A; (c) potential difference across the parallel combination of the and resistors V.
    Step-by-step solution →
  7. Q33 3 marks
    1. (a)Write the relationship between resistivity and resistance of a cylindrical conductor of length and area of cross-section . Hence derive the SI unit of resistivity.
    2. (b)Why are alloys used in electrical heating devices ?
    Show answer

    Resistivity is with SI unit ohm metre; alloys are used for heating because of high resistivity and resistance to oxidation.

    (a) For a cylindrical conductor of length and area of cross-section , , so the resistivity is . Substituting the SI units, unit of , so the SI unit of resistivity is the ohm metre (). (b) Alloys are used in electrical heating devices because the resistivity of an alloy is much higher than that of its constituent pure metals, so a wire of practical size has a large resistance and produces a large amount of heat (); and alloys such as nichrome do not oxidise or burn readily even at high temperatures, so the heating element lasts long.
    Step-by-step solution →

Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks
    1. (i)Draw two isomeric structures of Butene ().
    2. (ii)Name the following compounds :
    3. (iii)Write the chemical equations for the following reactions. Mention one essential condition each for these reactions to take place. (I) Ethanol undergoes complete oxidation (II) Propene undergoes hydrogenation (III) Ethanoic acid reacts with ethanol
    (I) H C C C Cl H H H H H H
    Structure (I)
    (II) H C C C C H H H H H H O H
    Structure (II)
    Show answer

    But-1-ene and but-2-ene; (I) 1-chloropropane, (II) butanone; ethanol burns in excess air, propene adds hydrogen over nickel, ethanoic acid and ethanol react with conc. sulphuric acid.

    (i) The two isomers are but-1-ene, , and but-2-ene, . (ii) (I) 1-Chloropropane, ; (II) Butanone (butan-2-one), . (iii) (I) , the essential condition being that the ethanol is burnt in a sufficient (excess) supply of oxygen or air. (II) , the essential condition being the presence of a nickel catalyst with warming. (III) , the essential condition being a few drops of concentrated sulphuric acid with gentle heating.
    Step-by-step solution →
    OR
    Q34(b) 5 marks
    1. (i)A carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer.
    2. (ii)Write chemical equation to show what happens when ethanol : (I) burns in oxygen/air. (II) is heated at 443 K in excess conc. . (III) reacts with acidified potassium dichromate.
    Show answer

    X is ethanol, Y sodium ethoxide, Z hydrogen; ethanol burns to carbon dioxide and water, dehydrates to ethene, and is oxidised to ethanoic acid.

    (i) is ethanol, ; is sodium ethoxide, ; and is hydrogen gas, , which hardens vegetable oil into vegetable ghee by hydrogenation over a nickel catalyst. The justifying equation is . (ii) (I) . (II) , with excess concentrated at K acting as the dehydrating agent. (III) with warm acidified , so ethanol is oxidised to ethanoic acid.
    Step-by-step solution →
  2. Q35(a) 5 marks

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

    1. (i)Write the functions of the following parts of human female reproductive system : (I) Ovary (II) Fallopian tube (III) Uterus
    2. (ii)State briefly two contraceptive methods used by human males.
    Show answer

    Ovary makes the ovum and hormones, fallopian tube is the site of fertilisation, uterus nourishes the foetus; condom and vasectomy are male methods.

    (i)(I) The ovary produces the female gametes, releasing one mature ovum about every month from puberty onwards, and it also secretes the female sex hormones oestrogen and progesterone, which bring about the secondary sexual characters and control the monthly changes in the uterine lining. (II) The fallopian tube (oviduct) collects the ovum from the ovary and carries it towards the uterus, and it is the site of fertilisation, where a sperm fuses with the ovum to form the zygote, which the tube then passes on to the uterus. (III) The uterus receives the embryo, whose implantation in its thickened lining begins pregnancy, and it nourishes and protects the developing embryo and foetus through the placenta until birth; if there is no fertilisation the lining is shed as menstruation. (ii) Two contraceptive methods used by human males are, first, the condom, a barrier method in which a thin sheath worn on the penis collects the semen so that the sperms are never deposited in the female reproductive tract, which also lowers the risk of sexually transmitted infections; and second, vasectomy, a surgical method in which a small portion of each vas deferens is cut out and the ends tied, so that sperms cannot pass from the testes into the semen and the semen released contains no sperms at all.
    Step-by-step solution →
    OR
    Q35(b) 5 marks

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

    1. (i)Differentiate between self-pollination and cross-pollination.
    2. (ii)Identify A, B and C in the diagram given below and write one function of each.
    A B C
    Show answer

    Self-pollination is within one plant, cross-pollination between plants; A is the stigma, B the pollen tube, C the female germ cell.

    (i) In self-pollination the pollen is transferred from the anther to the stigma of the same flower, or of another flower on the same plant, whereas in cross-pollination it is carried from the anther of a flower on one plant to the stigma of a flower on a different plant of the same kind. Self-pollination within a single flower is possible only in a bisexual flower, while cross-pollination occurs in unisexual flowers as well; within one flower it needs no external agent, while cross-pollination always requires wind, water, insects, birds or other animals; it involves one parent plant, while cross-pollination involves two; and its offspring are almost identical with the parent so that the variety stays pure, while the offspring of cross-pollination combine the characters of two parents, show new variations and are usually healthier and better adapted. (ii) A is the stigma, whose function is to receive the pollen grains at pollination and to provide the sticky, moist surface on which a grain germinates. B is the pollen tube, whose function is to carry the male germ cell from the pollen grain down through the style and into the ovule and deliver it to the female germ cell. C is the female germ cell, or egg, whose function is to fuse with the male germ cell in fertilisation and so form the zygote that grows into the embryo of the seed.
    Step-by-step solution →
  3. Q36(a) 5 marks

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

    1. (i)The power of a lens 'X' is D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens ?
    2. (ii)"The value of magnification for a lens is ." Using new Cartesian Sign Convention and considering that an object is placed at a distance of cm from the optical centre of this lens, state : (I) the nature of the image formed; (II) size of the image compared to the size of the object; (III) position of the image, and (IV) sign of the height of the image.
    3. (iii)The numerical values of the focal lengths of two lenses A and B are cm and cm respectively. Which one of the two will show higher degree of convergence/divergence ? Give reason to justify your answer.
    Show answer

    (i) Concave lens, cm, for myopia; (ii) real, inverted, magnified image at cm; (iii) lens A, the larger power.

    (i) The power is negative, so lens X is a concave (diverging) lens; its focal length is m cm, and an optician prescribes this type of lens to correct myopia (short-sightedness). (ii) With cm and , cm. (I) The image is real and inverted. (II) It is magnified — twice the size of the object. (III) It is formed cm from the optical centre, on the side of the lens opposite the object. (IV) The height of the image is negative, since . (The lens of this part must be a convex lens of focal length cm, because a concave lens can never give a magnification of .) (iii) Lens A, of focal length cm, shows the higher degree of convergence or divergence, because power is the reciprocal of focal length: D against D, so lens A bends the rays twice as strongly.
    Step-by-step solution →
    OR
    Q36(b) 5 marks

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

    1. (i)Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass.
    2. (ii)State Snell's law of refraction of light.
    3. (iii)Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of : (I) object distance, and (II) magnification.
    Show answer

    Emergent ray is parallel to the incident ray; a convex lens gives a virtual image only inside (), a concave lens always ().

    (i) The ray diagram is given above: the incident ray strikes the upper face of the slab, bends towards the normal inside the glass so that the angle of refraction is less than the angle of incidence , travels straight to the lower face, and there bends away from the normal as it re-enters air, emerging at an angle of emergence ; the emergent ray is therefore parallel to the incident ray but shifted sideways by the lateral displacement. (ii) Snell's law: when light passes obliquely from one medium to another, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media and for light of a given colour, that is , the refractive index of the second medium with respect to the first. (iii)(I) Object distance: a convex lens forms a virtual image only when the object is placed between its optical centre and its principal focus, whereas a concave lens forms a virtual image for every position of the object, from infinity right up to the optical centre. (II) Magnification: the virtual image formed by a convex lens is enlarged, with , while that formed by a concave lens is always diminished, with ; both images are erect and lie on the same side of the lens as the object.
    Step-by-step solution →

Questions 37–39 · 4 marks each

  1. Q37 4 marks

    Also in 31/1/2 (Q39), 31/1/3 (Q38)

    Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
    1. (a)Write balanced chemical equations to show the products formed during electrolysis of brine.[1]
    2. (b)List two uses of any one product obtained during electrolysis of brine.[1]
    3. (c)(i)A mild non-corrosive basic salt ‘A’, used for faster cooking, is strongly heated to produce a compound ‘B’, that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated.[2]
    4. (c)(ii)OR : Define water of crystallisation. Give two examples of salts that have water of crystallisation.[2]
    Show answer

    Brine electrolysis gives , and ; A is baking soda, B is sodium carbonate; water of crystallisation is fixed water in a salt.

    (a) - chlorine is given off at the anode, hydrogen at the cathode and sodium hydroxide solution is formed near the cathode. (b) Sodium hydroxide is used (i) in the manufacture of soaps and detergents and (ii) for de-greasing metals; paper making and artificial fibres are equally acceptable. (c)(i) A is sodium hydrogencarbonate, baking soda, ; B is sodium carbonate, , which after recrystallisation is washing soda, . The equation is . (c)(ii) Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt; two examples are copper sulphate pentahydrate and washing soda .
    Step-by-step solution →
  2. Q38 4 marks

    Also in 31/1/2 (Q38), 31/1/3 (Q39)

    The maintenance functions of all living organisms must go on even when they are not doing anything particular. Even when we are just sitting in a class or even asleep, this maintenance job has to go on. These maintenance processes require energy to prevent damage and break-down of cells and tissues, which is obtained by the individual organism from the food prepared by the autotrophs, called producers.
    1. (a)Name and define the process by which green plants prepare food.[1]
    2. (b)Write chemical equation involved in the above process.[1]
    3. (c)(i)State in proper sequence the events that occur in synthesis of food by desert plants.[2]
    4. (c)(ii)OR : Explain giving reasons what happens to the rate at which the green plants will prepare food (I) during cloudy weather, and (II) when stomata get blocked due to dust.[2]
    Show answer

    Photosynthesis makes carbohydrate from carbon dioxide and water; desert plants fix carbon dioxide at night; cloudy weather and blocked stomata lower the rate.

    (a) The process is photosynthesis: the process by which green plants (autotrophs) take in carbon dioxide and water and convert them into carbohydrates in the presence of sunlight and chlorophyll, releasing oxygen. (b) (the cancelled form is equally acceptable). (c)(i) At night the stomata open and carbon dioxide is taken in and fixed into an intermediate, which is stored; by day, with the stomata closed, chlorophyll absorbs light energy, that energy becomes chemical energy and water is split into hydrogen and oxygen, and the carbon dioxide from the stored intermediate is reduced to carbohydrate. (c)(ii) (I) During cloudy weather the rate decreases, because less light energy reaches the chlorophyll. (II) When the stomata are blocked by dust the rate decreases, because less carbon dioxide can enter the leaf.
    Step-by-step solution →
  3. Q39 4 marks

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

    In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V.
    1. (a)Write the colours of the insulation covers of the line wires through which supply comes to our homes.[1]
    2. (b)What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated ?[1]
    3. (c)(i)What is the function of the earth wire ? State the advantage of the earth wire in domestic electric appliances such as electric iron.[2]
    4. (c)(ii)OR : List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.[2]
    Show answer

    Live wire is red, neutral black; the iron needs a 5 A circuit ( A); the earth wire carries leakage current to the earth.

    (a) The live wire has a red insulation cover and the neutral wire a black insulation cover. (The earth wire is green, but it is not one of the two wires through which the supply comes.) (b) A, so the circuit must be able to carry at least this much: the standard A domestic circuit is required. (c)(i) The earth wire is connected to a metal plate buried deep in the earth and provides a low-resistance conducting path for the current to the earth. Its advantage is that the metal body of an appliance such as an electric iron is joined to it, so if the live wire touches the body the leakage current runs to the earth instead of through the user, the body stays at earth potential and the user escapes a severe shock (the large current also blows the fuse). (c)(ii) Two precautions: use a fuse of the correct rating in every circuit, which melts and breaks the circuit when overloading or a short circuit makes the current rise abruptly, so the appliance and the wiring are not damaged; and avoid connecting too many appliances to one socket and keep the insulation in good repair, so the current never exceeds what the wiring is rated for and the live and neutral wires cannot touch.
    Step-by-step solution →

Other 2025 papers

All CBSE Class 10 Science papers →