Science — Sample Paper SET 2 (Very Hard / HOTS)

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.

⚠️ This is a HOTS / very-difficult set — deliberately harder than the board paper. Attempt after mastering Set 1.

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 (b) Both true but R is NOT the correct explanation (c) A true, R false (d) A false, R true.

1. On heating, 5.0 g of CaCO₃ decomposes completely to give 2.8 g of CaO. Using the law of conservation of mass, the mass of CO₂ released is:
   (a) 2.2 g(b) 7.8 g(c) 2.8 g(d) 5.0 g
2. The pH of a 0.001 M solution of HCl (a strong acid) is:
   (a) 3(b) 11(c) 2(d) 1
3. Four metals P, Q, R and S: P displaces Q from its salt solution; R displaces P; S displaces none of them. The correct decreasing order of reactivity is:
   (a) R > P > Q > S(b) S > R > P > Q(c) Q > P > R > S(d) P > Q > R > S
4. Which pair of compounds will both decolourise bromine water?
   (a) ethene and ethyne(b) ethane and methane(c) ethane and ethene(d) methane and ethyne
5. The next higher homologue of ethanoic acid (CH₃COOH) is:
   (a) C₂H₅COOH(b) HCOOH(c) CH₃COOH(d) C₃H₇OH
6. The opening and closing of stomata is controlled by:
   (a) guard cells(b) chlorophyll content(c) xylem vessels(d) root pressure
7. A well-watered potted plant is placed in complete darkness; its rate of transpiration drops sharply. The most likely reason is:
   (a) the stomata close(b) the roots stop absorbing water(c) the xylem gets blocked(d) chlorophyll is destroyed
8. On touching a hot object we withdraw the hand instantly and feel the heat a moment later. This shows that:
   (a) a reflex action is quicker than a conscious response(b) the brain plays no part in any response(c) motor neurons are slower than sensory ones(d) the receptors are not working
9. Which mode of reproduction produces offspring with the least variation?
   (a) binary fission in Amoeba(b) sexual reproduction(c) cross-pollination(d) fertilisation of gametes
10. A couple already has three daughters. The probability that their fourth child will be a son is:
    (a) 1/2(b) 1/4(c) 1/8(d) 0
11. A concave mirror of focal length 20 cm produces a virtual image three times the size of the object. The object distance is:
    (a) 13.3 cm(b) 20 cm(c) 40 cm(d) 6.7 cm
12. Light of speed 3 × 10⁸ m/s in air enters a medium of refractive index 1.5. Its speed in the medium becomes:
    (a) 2 × 10⁸ m/s(b) 4.5 × 10⁸ m/s(c) 1.5 × 10⁸ m/s(d) 3 × 10⁸ m/s
13. Two thin lenses of power +3 D and −5 D are placed in contact. The power and nature of the combination are:
    (a) −2 D, diverging(b) +2 D, converging(c) −8 D, diverging(d) +8 D, converging
14. n identical resistors, each of resistance R, are joined first all in series and then all in parallel. The ratio (series resistance : parallel resistance) is:
    (a) n²(b) n(c) 1/n(d) 1/n²
15. An electric iron of resistance 20 Ω draws a current of 5 A. The heat produced in 30 s is:
    (a) 15,000 J(b) 3,000 J(c) 500 J(d) 100 J
16. DDT sprayed on a crop enters a food chain. It is found in the highest concentration in:
    (a) fish-eating birds(b) the crop plants(c) small fish(d) pond water
17. Assertion (A): Carbon forms an extremely large number of compounds.
    Reason (R): Carbon shows the properties of catenation and tetravalency.
18. Assertion (A): The urine of a healthy person normally contains no glucose.
    Reason (R): All the glucose filtered at the glomerulus is reabsorbed in the tubule of the nephron.
19. Assertion (A): Red light is used for danger signals.
    Reason (R): Red light is scattered the most by fog and air particles.
20. Assertion (A): The resistance of a metallic conductor increases when it is heated.
    Reason (R): On heating, the free electrons collide more frequently, opposing the flow of current.

SECTION B (Q21–26) — 2 marks each

21. 2A white salt, on strong heating, gives off a brown gas and a crackling sound, leaving a yellow residue that turns white on cooling. Identify (i) the salt and (ii) the brown gas.
22. 2The pH of rain water sometimes falls below 5.6. (i) What is such rain called? (ii) Name two gaseous oxides responsible and the type of compounds they form with rain water.
23. 2Herbivores usually have a much longer small intestine than carnivores. Give a reason based on the food they eat.
24. 2Name the plant hormone that (i) promotes cell elongation and growth towards light, and (ii) inhibits growth and helps in the closing of stomata / falling of leaves.
25. 2The magnification produced by a mirror for all positions of the object is +1. (i) Name the mirror. (ii) State the nature of the image.
26. 2Two resistors connected in series give a resistance of 9 Ω, and the same two in parallel give 2 Ω. Find the values of the two resistances.

SECTION C (Q27–33) — 3 marks each

27. 3A student claims: 'When zinc granules are added to dilute sulphuric acid, oxygen gas is evolved which burns with a pop sound.' (i) Identify and correct the two errors in this statement. (ii) Write the correct balanced chemical equation.
28. 3Give reasons: (i) Iron articles are painted. (ii) Aluminium does not corrode easily, although it is a fairly reactive metal. (iii) Sodium is far more reactive than iron.
29. 3A hydrocarbon burns (i) with a clean blue flame in plenty of air and (ii) with a yellow, sooty flame in a limited supply of air. Explain why, name the two kinds of combustion, and state which is more useful as a fuel and why.
30. 3Design a simple experiment (with a control) to demonstrate that carbon dioxide is released during respiration in germinating seeds. State the expected observation and the conclusion.
31. 3'In human beings, the sex of the child is determined by the father and not by the mother.' Justify this statement with the help of a cross showing the sex chromosomes of the parents and the possible children.
32. 3An object is placed 15 cm in front of a concave mirror of focal length 10 cm. Find the position and nature of the image and its magnification.
33. 3Three resistors of 4 Ω, 6 Ω and 12 Ω are available. Show with calculations how you would connect all three together to obtain (i) the maximum and (ii) the minimum possible equivalent resistance, and state each value.

SECTION D (Q34–36) — 5 marks each

34. 5(a) Why does carbon form mainly covalent compounds? (b) Draw the electron-dot (Lewis) structures of methane (CH₄), ethene (C₂H₄) and ethyne (C₂H₂). (c) Describe one chemical test to distinguish a saturated from an unsaturated hydrocarbon.
    OR
    (a) What is esterification? Write the equation for the reaction of ethanoic acid with ethanol. (b) What is saponification? (c) Explain, with a labelled idea of a micelle, how soap removes oily dirt.
35. 5(a) Draw a labelled diagram of a nephron. (b) Describe how urine is formed in the nephron (filtration and reabsorption). (c) Why is the process called selective reabsorption?
    OR
    (a) Draw a labelled longitudinal section of a flower. (b) Describe fertilisation in a flowering plant. (c) State what the ovule and the ovary become after fertilisation.
36. 5(a) Derive the expression P = V²/R for the power dissipated in a resistor. (b) An electric heater of power 1000 W is used for 2 hours daily. Calculate the electrical energy consumed in 30 days and its cost at ₹5 per unit. (c) Why is the heating element made of nichrome while the connecting wires are of copper?

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

37. 4Case Study: Iron objects rust in moist air; to protect food, potato-chip packets are flushed with an unreactive gas; and an iron railway bridge is repainted every few years.
    (i) Name the slow process by which the iron of the bridge is eaten away, and the compound formed. (1)
    (ii) Why are chips packets flushed with nitrogen rather than left with air? (1)
    (iii) Suggest and justify two different methods (other than painting) to protect the iron bridge from this process. (2)
38. 4Case Study: In a pond ecosystem the food chain is: algae → small fish → big fish → kingfisher. Sunlight trapped by the algae is 20,000 J.
    (i) What is the trophic level of the big fish? (1)
    (ii) Using the 10% law, how much energy reaches the kingfisher? (1)
    (iii) A pesticide is added to the pond. In which organism will it accumulate the most, and why? Name this phenomenon. (2)
39. 4Case Study: In a house, a 1000 W geyser, a 500 W iron and four 100 W bulbs are all switched on together on a 220 V line protected by a 5 A fuse.
    (i) State the function of a fuse in a circuit. (1)
    (ii) Calculate the total current drawn by all the appliances. (1)
    (iii) Will the 5 A fuse blow? Justify your answer with the calculation, and suggest what has gone wrong. (2)

Answer Key & Marking Scheme

Section A — MCQ (Q1–16)

1. (a) · 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. (a) · 18. (a) · 19. (c) — A is true, but R is false: red light is scattered the LEAST, so it travels farthest. · 20. (a)

Section B

21. (i) Lead nitrate, Pb(NO₃)₂; (ii) the brown gas is nitrogen dioxide (NO₂) (1+1). 2Pb(NO₃)₂ →Δ→ 2PbO(yellow) + 4NO₂↑ + O₂↑.
22. (i) Acid rain (1). (ii) Sulphur dioxide (SO₂) and nitrogen oxides (NOₓ); they dissolve to form sulphuric and nitric acids (1).
23. Herbivores eat plant food rich in cellulose, which is hard and slow to digest; a longer intestine gives more time and surface area for its complete digestion and absorption (2).
24. (i) Auxin (also gibberellin for elongation) (1). (ii) Abscisic acid (1).
25. (i) A plane mirror (1). (ii) The image is virtual, erect and of the same size as the object (1).
26. R₁ + R₂ = 9 and R₁R₂/(R₁+R₂) = 2 → R₁R₂ = 18 (1). So R₁, R₂ are roots of x² − 9x + 18 = 0 → x = 3 or 6. Hence 3 Ω and 6 Ω (1).

Section C

27. (i) Error 1: the gas evolved is hydrogen, not oxygen. Error 2: it is hydrogen (not oxygen) that burns with a 'pop' sound (1½). (ii) Zn + H₂SO₄ → ZnSO₄ + H₂↑ (1½).
28. (i) Paint keeps out air and moisture, preventing rusting (1). (ii) Aluminium forms a thin, hard, protective oxide layer (Al₂O₃) that stops further corrosion (1). (iii) Sodium loses its outer electron much more easily (more electropositive) and lies far above iron in the reactivity series (1).
29. In plenty of air, complete combustion occurs → CO₂ + H₂O + a clean blue flame and much heat. In limited air, incomplete combustion occurs → CO + unburnt carbon (soot) + a yellow sooty flame (1½). Complete combustion is more useful as a fuel because it releases more heat and no poisonous CO/soot (1½).
30. Take germinating seeds in a conical flask with a small test tube of KOH hanging inside; seal with a cork carrying a bent delivery tube dipped in water. Control: an identical flask with boiled (dead) seeds. Observation: in the flask with live seeds the KOH absorbs the CO₂ released, pressure falls, and water rises up the tube; no rise in the control (2). Conclusion: germinating (living) seeds respire and release CO₂ (1).
31. Mother is XX, father is XY. All eggs carry X; sperms are of two kinds, X or Y. Cross: XX × XY → children XX (girl) or XY (boy) in a 1:1 ratio (2). Since the mother always gives X, the child's sex depends on whether the father's sperm carries X or Y — hence the father determines the sex (1).
32. u = −15 cm, f = −10 cm. 1/v = 1/f − 1/u = −1/10 + 1/15 = (−3+2)/30 = −1/30 → v = −30 cm (real, in front of mirror) (1½). m = −v/u = −(−30)/(−15) = −2 → image is real, inverted and twice the size of the object, 30 cm in front of the mirror (1½).
33. (i) Maximum = all three in series = 4 + 6 + 12 = 22 Ω (1½). (ii) Minimum = all three in parallel: 1/R = 1/4 + 1/6 + 1/12 = (3+2+1)/12 = 1/2 → R = 2 Ω (1½).

Section D

34. (a) Carbon has 4 valence electrons; losing or gaining 4 electrons needs too much energy, so it shares electrons and forms covalent bonds (1). (b) Correct Lewis structures: CH₄ (4 single bonds), C₂H₄ (C=C double bond), C₂H₂ (C≡C triple bond) (½×3). (c) Add bromine water: the unsaturated hydrocarbon decolourises it; the saturated one does not (1½). OR (a) esterification = acid + alcohol → ester + water; CH₃COOH + C₂H₅OH →(H₂SO₄)→ CH₃COOC₂H₅ + H₂O (2). (b) saponification = alkaline hydrolysis of a fat/oil to give soap + glycerol (1). (c) soap's hydrophobic tail dissolves in oil, hydrophilic head faces water → forms a micelle that traps the dirt and is washed away (2).
35. (a) Correct labelled nephron: glomerulus, Bowman's capsule, tubule, collecting duct (2). (b) Blood is filtered at the glomerulus; the filtrate passes into the tubule, where useful substances (glucose, salts, water) are reabsorbed, and the remaining waste forms urine (2). (c) 'Selective' because only useful materials are reabsorbed, wastes like urea are left behind (1). OR (a) labelled flower (2); (b) pollen tube carries male gametes to the ovule; one gamete fuses with the egg → zygote (fertilisation) (2); (c) ovule → seed, ovary → fruit (1).
36. (a) P = VI and V = IR → P = (IR)I = I²R = (V/R)²R = V²/R (2). (b) Energy = 1 kW × 2 h × 30 = 60 kWh (units); cost = 60 × ₹5 = ₹300 (2). (c) Nichrome has high resistivity and a high melting point, so it produces heat without melting; copper has very low resistance, so it carries current without heating (1).

Section E

37. (i) Corrosion (rusting); the compound is hydrated iron(III) oxide, Fe₂O₃·xH₂O (rust) (1). (ii) Nitrogen is unreactive; it keeps out oxygen and moisture and so prevents oxidation/rancidity of the fried chips (1). (iii) Any two, justified: galvanisation (coat with zinc, which corrodes in preference to iron); greasing/oiling or electroplating (barrier to air & moisture); alloying (e.g. stainless steel) (2).
38. (i) The big fish is a tertiary consumer / third-order consumer (fourth trophic level) (1). (ii) 20,000 → 2,000 → 200 → 20 J reaches the kingfisher (1). (iii) It accumulates most in the kingfisher (top of the chain), because the non-degradable pesticide is passed on and concentrated at each level; this is called biological magnification (2).
39. (i) A fuse melts and breaks the circuit when the current exceeds a safe value, protecting the wiring/appliances (1). (ii) Total power = 1000 + 500 + 4×100 = 1900 W; I = P/V = 1900/220 = 8.6 A (1). (iii) Since 8.6 A > 5 A, the fuse will blow. The circuit is overloaded — too many high-power appliances on one line; use separate circuits or a higher-rated line (2).