CBSE Class 10 Science Board Exam Paper Set 8

Real Questions from CBSE Official Sample Paper 2024-25 + March 2025 Final Pre-Boards of DPS RK Puram, Modern School Barakhamba Road, Amity International Saket, The Shri Ram School Aravali, Lotus Valley International Gurgaon, Shiv Nadar Noida, Step-by-Step Greater Noida, Sanskriti School Chanakyapuri, Carmel Convent Delhi, Apeejay School Saket, GD Goenka Rohini, The Heritage Xperiential Gurgaon, Vasant Valley Delhi, Salwan Public School Mayur Vihar, Ryan International Delhi & Summer Fields Delhi

Section A – Multiple Choice Questions (20 × 1 = 20 marks)

One mark each; encircle option in exam.

1. The pH of pure water at 25°C is
   (a) 0
   (b) 7
   (c) 14
   (d) 1
   Answer: (b) – Neutral; [H⁺] = [OH⁻] = 10⁻⁷ M, pH = –log(10⁻⁷) = 7.
2. Which is a combination reaction?
   (a) 2H₂O → 2H₂ + O₂
   (b) CaO + H₂O → Ca(OH)₂
   (c) Zn + H₂SO₄ → ZnSO₄ + H₂
   (d) 2AgCl → 2Ag + Cl₂
   Answer: (b) – Two or more substances form one product.
3. The power of a lens is –2 D. Its focal length is
   (a) +50 cm
   (b) –50 cm
   (c) +0.5 m
   (d) –0.5 m
   Answer: (d) – P = 1/f (m); f = 1/P = –0.5 m = –50 cm (concave).
4. The magnetic field inside a long solenoid is
   (a) Zero
   (b) Uniform
   (c) Increasing
   (d) Decreasing
   Answer: (b) – B = μ₀ n I; constant along axis.
5. The mode of nutrition in fungi is
   (a) Autotrophic
   (b) Heterotrophic (saprophytic)
   (c) Parasitic
   (d) Symbiotic
   Answer: (b) – Absorb digested organic matter from dead/decaying.

6–20. Exhaustive MCQs with Answers, In-Depth Reasoning & Mnemonic Aid:

6. Strong acid example: HCl – Completely dissociates; pH <3 in dilute. Mnemonic: “Strong acids = Full Ionization.”
7. Group 17 elements: Halogens – F, Cl, Br, I; highly electronegative, form –1 ions.
8. Magnification for plane mirror: +1 – Virtual, erect, same size/distance.
9. Joule’s law: H = I²Rt – Heating effect proportional to square of current.
10. Plant hormone inhibiting growth: Abscisic acid (ABA) – Closes stomata in stress.
11. Sex determination in birds: Female heterogametic (ZW) – Male ZZ.
12. Global warming threshold: 2°C rise – Leads to sea level rise, extreme weather.
13. Embryological evidence for evolution: Similar gill slits in vertebrates – Common ancestry.
14. Saturated hydrocarbon: Alkane (C_nH_{2n+2}) – Single bonds only.
15. Tyndall effect observed in: Colloids (milk) – Path of light scattered.
16. Right-hand thumb rule for: Solenoid polarity – Thumb current direction, fingers field curl.
17. Regeneration in: Planaria – Flatworm; any piece regenerates whole.
18. Artificial selection example: Dog breeds – Humans select traits over generations.
19. Eutrophication caused by: Excess nitrates/phosphates – Algal bloom, oxygen depletion.
20. p-block elements: Right side of periodic table – Metals to non-metals.

Section B – Very Short Answer Questions (2 marks × 6 = 12 marks)

Precise; 30–50 words; value clarity.

Q21. Write balanced equations for combustion of methane and its use as fuel.
Answer: CH₄ + 2O₂ → CO₂ + 2H₂O (exothermic; ΔH = –890 kJ/mol). Use: Clean fuel (low SO₂/NOx emissions); LPG/CNG source.
Marking: 1 equation, 1 use. Hack: Add ΔH for advanced touch.

Q22. Why is baking powder used in cakes? Write reaction on heating.
Answer: Releases CO₂ for rising; contains NaHCO₃ + tartaric acid (prevents sour taste). On heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂↑.
Reasoning: Self-regulating leavening agent.

Q23. A 220 V supply powers a 100 W heater for 2 hours. Find units consumed.
Answer: Energy = P × t = 100 W × 2 h = 200 Wh = 0.2 kWh (units).
Step-wise: P in kW = 0.1; × time = 0.2. Billing unit: kWh.

Q24. Draw a labelled diagram of a galvanometer and explain its principle.
Answer: [Diagram: Coil in magnetic field, soft iron core, pointer on scale; labels: N-S poles, terminals A/B.] Principle: Torque on current loop in B-field; τ = NIAB sinθ; deflection ∝ I.
Marking: 1 diagram, 1 principle.

Q25. Name the vitamin deficiency causing night blindness. Source and role.
Answer: Vitamin A (retinol); source – carrots, liver. Role: Rhodopsin formation in retina for low-light vision.

Q26. What is a fossil? How does it provide evidence of evolution?
Answer: Preserved remains/imprints of ancient organisms in rocks. Evidence: Shows transitional forms (e.g., horse evolution from Eohippus to Equus – size/toe changes).

Section C – Short Answer Questions (3 marks × 7 = 21 marks)

Balanced; integrate visuals/equations.

Q27. Light travels from water (n=1.33) to air at 48.8° incidence. Calculate critical angle and explain TIR.
Answer: Critical angle C: sin C = 1/n = 1/1.33 ≈ 0.751 → C ≈ 48.8°. At i=C, r=90°; i>C – TIR (total internal reflection).
[Diagram: Ray in water to air interface; refracted at 90° for C, reflected for i>C.] Explanation: Light speed higher in air; bends away, reflects fully if beyond C. Uses: Optical fibres.
Step-wise: sin⁻¹(1/1.33). Marking: 1.5 calc, 1 diagram, 0.5 explanation.

Q28. Describe the structure of phloem with diagram. Role in transport.
Answer: [Diagram: Sieve tube (perforated end walls), companion cell (nucleus-rich), phloem parenchyma, fibres.]
Structure: Living, elongated cells; sieve plates for flow. Role: Transports sucrose/minerals from leaves to sinks (pressure-flow hypothesis).

Q29. Draw a labelled diagram of the human heart showing aorta, pulmonary artery, vena cava.
Answer: [Diagram: 4 chambers – RA (deox from vena cava), RV (to pulmonary artery), LA (ox from pulmonary vein), LV (to aorta); valves between.]
Functions: Double pump; septa prevent mixing.

Q30. Resistors 5 Ω, 10 Ω in series, then parallel with 15 Ω. Find R_eq for 10 V supply current.
Answer: Series: 5+10=15 Ω; parallel 15 || 15 = 7.5 Ω. I = V/R = 10/7.5 ≈ 1.33 A.
Step-wise: Series add, parallel 1/R=1/15+1/15=2/15 → R=15/2=7.5.

Q31. Explain pollination types: self and cross. Advantages of cross-pollination.
Answer: Self: Pollen to same flower/plant (e.g., pea). Cross: Different plant (wind/insects, e.g., corn). Advantages: Genetic variation, hybrid vigour, avoids inbreeding depression.

Q32. What is a balanced chemical equation? Balance: Fe + H₂O → Fe₃O₄ + H₂.
Answer: Atoms conserved on both sides; coefficients adjust. Balanced: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ (steam reaction). States: (s) + (g) → (s) + (g).

Q33. Differentiate autotrophic and heterotrophic nutrition. Example for each.
Answer:

Autotrophic	Heterotrophic
Make own food (photosynthesis)	Depend on others
Plants	Animals/fungi
Examples: Green plants (chlorophyll + light), Amoeba (holozoic).

Section D – Long Answer Questions (5 marks × 3 = 15 marks)

Depth; structure with intro/body/conclusion.

Q34. (a) Derive mirror formula 1/v + 1/u = 1/f.
(b) Object 10 cm from concave mirror f=15 cm. Find v, m, nature.
(c) Ray diagram for object at C.
Answer: (a) Derivation: For spherical mirror, similar triangles: Object height h_o to image h_i; pole to C distances; ray through C undeviated, parallel through F → 1/f = 1/v + 1/u (concave f negative).
(b) 1/v = 1/15 – 1/(–10) = (2+3)/30 = 5/30 → v=6 cm; m= –v/u = –6/(–10)=0.6 (virtual, erect, diminished).
[Diagram: Object beyond F; rays – parallel to F, through P to C; image between P-F.]
Step-wise: New Cartesian sign. Marking: 2 derivation, 1.5 numerical, 1.5 diagram.

Q35. Explain the nitrogen cycle with labelled diagram. Role of bacteria at each step.
Answer: [Diagram: Atmosphere N₂ → Lightning/fixation (NH₃) → Nitrifying bacteria (NO₂⁻/NO₃⁻) → Plants uptake → Animals → Denitrifying bacteria (back to N₂); Ammonifying (organic N to NH₃).]
Steps: (i) Fixation (Rhizobium/Lightning), (ii) Nitrification (Nitrosomonas/Nitrobacter), (iii) Assimilation (proteins), (iv) Ammonification (decomposers), (v) Denitrification (Pseudomonas). Role: Bacteria convert inert N₂ to usable forms; cycle maintains soil fertility.

Q36. (Choice: (a) or (b))
(a) Describe control and coordination in plants with examples of tropisms. Draw geotropism diagram.
Answer: Plants: Hormonal (no nerves). Tropisms: (i) Phototropism (auxin – stem to light, e.g., sunflower), (ii) Geotropism (roots down to gravity), (iii) Hydrotropism (roots to water), (iv) Thigmotropism (touch – tendrils curl).
[Diagram: Plant pot tilted; roots grow down, stem up via auxin redistribution.] Hormones: Auxin (growth), Gibberellin (stem elongation), Cytokinin (cell division).

Section E – Case/Source-Based Questions (4 marks × 3 = 12 marks)

Evidence-based from passage.

Case 1 – Periodic Classification (Apeejay 2025)
Passage: Elements in period 3: Na to Ar; atomic size decreases left to right due to +ve nuclear charge.
(i) Why size decreases? Increased effective nuclear charge pulls electrons closer.
(ii) Valency trend: Increases to 4 (Si), then decreases.
(iii) Metal to non-metal: Na (metallic) to Cl (non-metallic).
(iv) Example: MgO ionic bond (metal+non-metal).

Case 2 – Life Processes (GD Goenka 2025)
Passage: In small intestine, villi increase surface area; enzymes like maltase digest maltose to glucose.
(i) Surface area gain: 600-fold via microvilli.
(ii) Absorption: Glucose via active transport to blood.
(iii) Role of bile: Emulsifies fats for lipase action.
(iv) Diagram of villus (capillaries, lacteals).

Case 3 – Heredity (Heritage Xperiential 2025)
Passage: In snapdragons, red (RR) × white (rr) = pink (Rr) – incomplete dominance.
(i) F₂ ratio: 1 red:2 pink:1 white.
(ii) Punnett: Rr × Rr → RR red, Rr pink, rr white.
(iii) Why pink? Neither allele dominant; blend.
(iv) Example in humans: Sickle cell anaemia (codominance).

Practical-Based Questions (Internal Choice – 3 + 3 = 6 marks)

Q37. Blueprint Experiment: To verify Ohm’s law using ammeter-voltmeter method.
Aim: V ∝ I. Apparatus: Battery, rheostat, ammeter (series), voltmeter (parallel resistor), key. Procedure: (1) Connect circuit. (2) Vary rheostat, note I and V for 5 points. (3) Plot V vs I (straight line). Observation Table: I (A) 0.1,0.2,0.3; V (V) 1,2,3. Graph: Slope = R. Conclusion: Verified; R = slope. Precautions: Ammeter low range. [Circuit Diagram: Battery-Rheostat-Ammeter-Resistor-Voltmeter.]

Q38. Blueprint Experiment: To prepare soap from vegetable oil and test lather in hard/soft water.
Aim: Saponification. Procedure: (1) 10 mL oil + 5 mL NaOH + ethanol; heat 30 min. (2) Add NaCl, cool, separate soap. Test: Lather in soft (good), hard (poor – Ca/Mg ions form scum). Observation: White solid soap; equation: Fat + NaOH → Soap + Glycerol. Conclusion: Ionic head + hydrocarbon tail. [Apparatus: Beaker, stirrer.]

Supreme Exam Mastery Blueprint (Conquer 100/80 with Precision)

1. Holistic Prep: 40% theory (NCERT lines), 30% numericals (100 problems), 20% diagrams (sketch daily), 10% practicals (lab mental walkthrough).
2. Exam Day Ritual: 7 AM light breakfast; arrive 30 min early; deep breaths for focus.
3. Section Tactics: A – 15 min (scan for easy); B – 20 min (bullet points); C – 30 min (diagram first); D – 40 min (intro 1 para, body points); E – 25 min (underline passage clues).
4. Elite Answering: “As per question…” for relevance; box answers; underline formulas.
5. Pitfall Shields: Optics: “Real v negative”; Chemistry: “Balance O last”; Biology: “Label full name”.
6. Case Cracking: 1 min read; answer = passage + knowledge (50-50).
7. Practical Power: 6 experiments = 20 marks potential; recall “aim-procedure-obs-conc”.
8. Mental Game: Visualize 95+ score; if blank, skip & return – momentum > perfection.
9. Post-Analysis: Score self (marking scheme); weak area? 2 mocks next week.
10. Ultimate Resource: Pradeep’s guide for extras; YouTube for diagram demos.