Science — Sample Paper SET 1 (Hard)

General Instructions

(i) All questions are compulsory. (ii) The paper has 5 sections A–E and 39 questions. (iii) Section A: Q1–20 carry 1 mark (16 MCQ + 4 Assertion–Reason). Section B: Q21–26 carry 2 marks. Section C: Q27–33 carry 3 marks. Section D: Q34–36 carry 5 marks. Section E: Q37–39 are case-based, 4 marks. (iv) Internal choice is provided in some questions. Draw neat diagrams where needed.

SECTION A (Q1–20) — 1 mark each

Q1–16 Multiple Choice · Q17–20 Assertion–Reason. For Q17–20 choose: (a) Both A and R true and R is the correct explanation of A (b) Both true but R is NOT the correct explanation (c) A true, R false (d) A false, R true.

1. A strip of copper is dipped in silver nitrate solution. After some time the solution turns blue and a shiny grey deposit forms on the copper. Which statement is INCORRECT?
   (a) Copper is oxidised(b) Silver ion is reduced(c) Copper is more reactive than silver(d) Silver has displaced copper
2. The reaction 3MnO₂ + 4Al → 3Mn + 2Al₂O₃ is best classified as:
   (a) a displacement and redox reaction(b) a combination reaction(c) a decomposition reaction(d) a double displacement reaction
3. Equal volumes of two solutions of pH = 3 and pH = 5 are mixed. The pH of the resulting mixture is closest to:
   (a) between 3 and 4(b) exactly 4(c) 8(d) 5
4. A metal M is kept under kerosene, reacts violently with cold water, and its oxide dissolves in water to give a strongly basic solution. M is most likely:
   (a) sodium(b) aluminium(c) iron(d) copper
5. The number of structural isomers of C₄H₁₀ and C₅H₁₂ respectively are:
   (a) 2 and 3(b) 3 and 2(c) 2 and 2(d) 3 and 3
6. In which of these vessels/vessels' blood is the oxygen content the highest?
   (a) pulmonary vein(b) pulmonary artery(c) vena cava(d) right ventricle
7. During vigorous exercise, when oxygen supply to muscle cells is insufficient, pyruvate is converted into:
   (a) lactic acid(b) ethanol and CO₂(c) CO₂ and water(d) glucose
8. The correct sequence of components of a reflex arc is:
   (a) receptor → sensory neuron → spinal cord → motor neuron → effector(b) effector → motor neuron → brain → sensory neuron → receptor(c) receptor → motor neuron → spinal cord → sensory neuron → effector(d) receptor → spinal cord → brain → effector
9. A gardener wants every new plant to be genetically identical to a prize rose. He should use:
   (a) vegetative propagation(b) seeds from cross-pollination(c) seeds from self-pollination(d) spore formation
10. A violet-flowered pea plant of genotype Vv is crossed with a white-flowered plant (vv). The probability of obtaining a white-flowered offspring is:
    (a) 1/2(b) 1/4(c) 3/4(d) 0
11. An object is placed exactly at the centre of curvature (C) of a concave mirror. The image formed is:
    (a) at C, real, inverted and of the same size(b) at F, real and diminished(c) virtual and magnified(d) at infinity
12. A convex lens forms a real image with magnification −0.5. If the object is placed 30 cm from the lens, its focal length is:
    (a) 10 cm(b) 15 cm(c) 20 cm(d) 6 cm
13. A person can see distant objects clearly but cannot read a book held close. The defect and the corrective lens are:
    (a) hypermetropia, convex lens(b) myopia, concave lens(c) presbyopia, bifocal lens(d) astigmatism, cylindrical lens
14. A uniform wire of resistance R is stretched (at constant volume) until its length is doubled. Its new resistance is:
    (a) 4R(b) 2R(c) R/2(d) R/4
15. A 60 W and a 100 W bulb (both rated 220 V) are connected in series across a 220 V supply. Which bulb glows brighter?
    (a) the 60 W bulb(b) the 100 W bulb(c) both glow equally(d) neither glows
16. In a food chain, 10,000 J of energy is available at the producer level. The energy available to a secondary consumer (following the 10% law) is:
    (a) 100 J(b) 1000 J(c) 10 J(d) 10,000 J
17. Assertion (A): When dilute HCl is added to NaOH solution, the temperature of the mixture rises.
    Reason (R): Neutralisation reactions are endothermic.
18. Assertion (A): Arteries have thick, elastic muscular walls.
    Reason (R): Arteries carry blood away from the heart under high pressure.
19. Assertion (A): A convex mirror is preferred as a rear-view mirror in vehicles.
    Reason (R): A convex mirror always forms a virtual, erect and diminished image and gives a wide field of view.
20. Assertion (A): The metallic body of an electric appliance is connected to the earth wire.
    Reason (R): The earth wire has a very high resistance.

SECTION B (Q21–26) — 2 marks each

21. 22 g of ferrous sulphate crystals are heated strongly in a dry boiling tube. (i) Name the type of chemical reaction. (ii) State the colour change and name one gas evolved.
22. 2Dilute HCl is added separately to Mg, Zn, Fe and Cu. Arrange the metals in decreasing order of the vigour of reaction, and name the metal that shows no reaction. Justify using the reactivity series.
23. 2The rate of breathing in aquatic organisms is much faster than in terrestrial organisms. Give two reasons.
24. 2A destarched potted plant is partly covered with black paper and kept in sunlight for a few hours. When tested with iodine, only the uncovered part turns blue-black. What does this prove, and why did the covered part not respond?
25. 2The power of a lens is +2.5 D. (i) Find its focal length. (ii) State its nature and one use.
26. 2Draw the pattern of magnetic field lines around a long straight current-carrying conductor and state the rule used to find their direction.

SECTION C (Q27–33) — 3 marks each

27. 3A student wrote the equation for zinc reacting with dilute hydrochloric acid as: 'Zn + 2HCl → ZnCl + H₂'. (i) Identify the error(s). (ii) Write the correct balanced equation. (iii) Name the type of reaction.
28. 3Give reasons: (i) A green coating forms on copper articles left in moist air. (ii) Food cans are coated with tin and not with zinc. (iii) Iron gates are painted regularly.
29. 3An organic compound X of molecular formula C₂H₆O reacts with sodium metal to release a gas that burns with a 'pop' sound; on warming with excess conc. H₂SO₄ at 443 K it gives an unsaturated compound Y. (i) Identify X and Y. (ii) Write the equation for the reaction of X with sodium.
30. 3(i) Trace the path of urine from its site of formation to its removal from the body. (ii) Name the structural and functional unit of the kidney. (iii) In a healthy person, what happens to the glucose that is filtered in the kidney?
31. 3In pea plants, round seed shape (R) is dominant over wrinkled (r) and yellow colour (Y) over green (y). A pure round-yellow plant is crossed with a wrinkled-green plant. (i) Give the genotype and phenotype of the F₁ plants. (ii) State the F₂ phenotypic ratio and what it demonstrates.
32. 3An object 4 cm high is placed 20 cm in front of a convex lens of focal length 10 cm. Using the lens formula, find the position, size and nature of the image.
33. 3Two resistors of 6 Ω and 3 Ω are connected across a 6 V battery, (i) in series and (ii) in parallel. Calculate the current drawn from the battery in each case.

SECTION D (Q34–36) — 5 marks each

34. 5(a) Name the four main types of chemical reactions and give one balanced equation for each. (b) Define a redox reaction and, in the reaction CuO + H₂ → Cu + H₂O, identify the substance oxidised and the substance reduced, with reasons.
    OR
    (a) What is meant by the pH of a solution? (b) Explain, with one example each, the importance of pH in (i) our digestive system, (ii) tooth decay, (iii) survival of aquatic life, and (iv) self-defence in plants/animals. (c) Why should water be added to acid and not acid to water?
35. 5(a) Draw a labelled diagram of the human heart. (b) Explain what is meant by double circulation and trace the path of blood through it. (c) Why is double circulation necessary in humans and birds?
    OR
    (a) Draw a labelled diagram of the human respiratory system. (b) Describe how the exchange of gases takes place in the alveoli. (c) Give two features that make the alveoli well-suited for gas exchange.
36. 5(a) State Ohm's law and draw a labelled circuit diagram to verify it. (b) Derive the expression for the equivalent resistance of three resistors connected in parallel. (c) Calculate the equivalent resistance when resistors of 2 Ω, 3 Ω and 6 Ω are connected in parallel.

SECTION E (Q37–39) — Case-based, 4 marks each

37. 4Case Study: At a science exhibition a student mixes a colourless solution of lead nitrate with a colourless solution of potassium iodide. A bright yellow solid appears at once and settles down. At another stall, a strip of zinc dipped in copper sulphate solution slowly turns brownish and the blue colour fades.
    (i) Name the yellow solid formed in the first experiment and write the balanced equation. (1)
    (ii) What type of reaction is the first one? (1)
    (iii) A student claims both experiments are redox reactions. Do you agree? Justify your answer for each. (2)
38. 4Case Study: The table shows the approximate pH in parts of the human alimentary canal — mouth 6.8, stomach 1.5, small intestine 8.0. Food is acted on by different enzymes in each region.
    (i) Name the enzyme present in saliva and the food it digests. (1)
    (ii) Why is the medium of the stomach strongly acidic? (1)
    (iii) A patient's small intestine has pH 5 instead of 8. Predict, with reasons, two effects this would have on digestion. (2)
39. 4Case Study: A Class-10 student finds she can read her book easily but cannot clearly see the writing on the board. An eye test shows the far point of her eye is only 2 m instead of infinity.
    (i) Name the defect and the type of lens used to correct it. (1)
    (ii) Calculate the power of the lens required to correct this defect. (1)
    (iii) Explain, with a ray-diagram idea, why the image of a distant object forms in front of the retina in this defect. (2)

Answer Key & Marking Scheme

Section A — MCQ (Q1–16)

1. (d) · 2. (a) · 3. (a) · 4. (a) · 5. (a) · 6. (a) · 7. (a) · 8. (a) · 9. (a) · 10. (a) · 11. (a) · 12. (a) · 13. (a) · 14. (a) · 15. (a) · 16. (a)

Section A — Assertion–Reason (Q17–20)

17. (c) — A is true, but R is false: neutralisation is exothermic (heat is released). · 18. (a) · 19. (a) · 20. (c) — A is true, but R is false: the earth wire has very LOW resistance.

Section B

21. (i) Thermal decomposition (1). (ii) Green FeSO₄ crystals turn brown/reddish (Fe₂O₃); gases SO₂ and SO₃ (smell of burning sulphur) are evolved (1). 2FeSO₄ →Δ→ Fe₂O₃ + SO₂ + SO₃.
22. Decreasing vigour: Mg > Zn > Fe > Cu (1). Cu shows no reaction because it is below hydrogen in the reactivity series and cannot displace H₂ from acids (1).
23. (1+1) Water contains far less dissolved oxygen than air; and oxygen diffuses more slowly in water — so organisms must pass more water over their gills, i.e. breathe faster, to get enough oxygen.
24. It proves that light is essential for photosynthesis (starch is made only where light fell) (1). The covered part received no light, so no photosynthesis and no starch — it did not turn blue-black (1).
25. (i) f = 1/P = 1/2.5 = 0.4 m = +40 cm (1). (ii) Positive → convex (converging) lens; used as a magnifying glass / to correct hypermetropia (1).
26. Concentric circles around the wire, closer near the wire and wider away from it (1). Direction is found by Right-hand thumb rule (Maxwell's corkscrew rule) (1).

Section C

27. (i) 'ZnCl' is wrong — zinc chloride is ZnCl₂ (Zn is divalent) (1). (ii) Zn + 2HCl → ZnCl₂ + H₂↑ (1). (iii) Displacement (and redox) reaction (1).
28. (i) Moist air contains CO₂ and moisture; copper forms basic copper carbonate CuCO₃·Cu(OH)₂, the green coat (1). (ii) Zinc is more reactive than tin and would react with the acids in food, contaminating it; tin is less reactive and safe (1). (iii) Paint keeps out air and moisture, preventing rusting (corrosion) (1).
29. (i) X = ethanol (C₂H₅OH); the pop gas is H₂; Y = ethene (C₂H₄) (1+1). (ii) 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑ (1).
30. (i) Nephron (kidney) → ureter → urinary bladder → urethra → out of the body (1). (ii) Nephron (1). (iii) The filtered glucose is completely reabsorbed back into the blood in the tubule (selective reabsorption) (1).
31. (i) F₁ genotype RrYy, phenotype round and yellow (all) (1+½). (ii) F₂ phenotypic ratio = 9 : 3 : 3 : 1 (round-yellow : round-green : wrinkled-yellow : wrinkled-green) (1); it shows the independent inheritance of the two traits (½).
32. u = −20 cm, f = +10 cm. 1/v = 1/f + 1/u = 1/10 + 1/(−20) = 1/20 → v = +20 cm (1). m = v/u = 20/(−20) = −1 → h′ = m·h = −4 cm (1). Image is real, inverted, same size (4 cm), 20 cm on the other side of the lens (1).
33. (i) Series: R = 6 + 3 = 9 Ω; I = V/R = 6/9 = 0.67 A (1½). (ii) Parallel: 1/R = 1/6 + 1/3 = 1/2 → R = 2 Ω; I = 6/2 = 3 A (1½).

Section D

34. (a) Combination: 2Mg+O₂→2MgO ; Decomposition: CaCO₃→CaO+CO₂ ; Displacement: Zn+CuSO₄→ZnSO₄+Cu ; Double displacement: AgNO₃+NaCl→AgCl↓+NaNO₃ (½×4=2). (b) A redox reaction is one in which oxidation and reduction occur simultaneously (1). In CuO+H₂→Cu+H₂O: CuO is reduced (loses oxygen) and H₂ is oxidised (gains oxygen) (2). OR (a) pH measures the H⁺-ion concentration; pH<7 acidic, =7 neutral, >7 basic (1). (b) (i) excess stomach acid → acidity, cured by antacids; (ii) tooth decay below pH 5.5; (iii) aquatic life dies if water pH changes (acid rain); (iv) bee sting acidic → baking soda (4×½=2, plus reasoning 1). (c) Adding acid to water dilutes the large heat released slowly and safely; the reverse can cause violent spurting (1).
35. (a) Correct labelled heart: right/left atria & ventricles, aorta, pulmonary artery/vein, vena cava, valves (2). (b) Double circulation = blood passes through the heart twice per cycle — pulmonary (heart→lungs→heart) and systemic (heart→body→heart) (2). (c) It keeps oxygenated and deoxygenated blood separate, giving an efficient oxygen supply needed by warm-blooded animals with high energy demand (1). OR (a) labelled respiratory system (2); (b) O₂ from alveolar air diffuses into blood, CO₂ diffuses out, due to concentration/pressure differences (2); (c) thin walls + large surface area + rich blood-capillary supply (1).
36. (a) Ohm's law: V ∝ I at constant temperature, i.e. V = IR; correct circuit with cell, ammeter (series), voltmeter (parallel), resistor, key (2). (b) In parallel V is same; I = I₁+I₂+I₃ = V/R₁+V/R₂+V/R₃ = V/R → 1/R = 1/R₁+1/R₂+1/R₃ (2). (c) 1/R = 1/2+1/3+1/6 = (3+2+1)/6 = 1 → R = 1 Ω (1).

Section E

37. (i) Lead iodide (PbI₂); Pb(NO₃)₂ + 2KI → PbI₂↓ + 2KNO₃ (1). (ii) Double displacement / precipitation reaction (1). (iii) The first is NOT redox — only ions are exchanged, no element changes its oxidation state / no gain-loss of oxygen. The second (Zn + CuSO₄ → ZnSO₄ + Cu) IS redox — Zn is oxidised and Cu²⁺ is reduced (2).
38. (i) Salivary amylase; it digests starch (into maltose) (1). (ii) The stomach secretes HCl to kill germs, activate pepsin and provide the acidic medium for protein digestion (1). (iii) At pH 5 the intestine is not alkaline enough: (a) bile and pancreatic lipase cannot emulsify/digest fats properly; (b) trypsin and intestinal enzymes (which need an alkaline medium) work poorly, so protein/carbohydrate digestion is incomplete → poor absorption (2).
39. (i) Myopia (near-sightedness); corrected with a concave (diverging) lens (1). (ii) The lens must have its focal length equal to the far point: f = −2 m; P = 1/f = −0.5 D (1). (iii) In myopia the eyeball is too long (or the lens too converging), so parallel rays from a distant object are brought to a focus in front of the retina, and the image on the retina is blurred; a concave lens diverges the rays so that they focus on the retina (2).