CBSE Class 10 Science Board Paper Set 7

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.

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

Each question carries 1 mark. Select the correct alternative.

1. The chemical formula of slaked lime is
   (a) CaO
   (b) CaCO₃
   (c) Ca(OH)₂
   (d) CaSO₄·2H₂O
   Answer: (c) – Slaked lime is calcium hydroxide, formed by adding water to quicklime (CaO + H₂O → Ca(OH)₂).
2. Which non-metal is a good conductor of electricity?
   (a) Sulphur
   (b) Carbon (graphite)
   (c) Iodine
   (d) Bromine
   Answer: (b) – Graphite has delocalised electrons for conduction, unlike diamond.
3. The principal focus of a convex mirror is
   (a) Behind the mirror
   (b) In front of the mirror
   (c) At the pole
   (d) At infinity
   Answer: (a) – Virtual focus for diverging rays.
4. The potential difference across a 10 Ω resistor with 2 A current is
   (a) 5 V
   (b) 10 V
   (c) 20 V
   (d) 12 V
   Answer: (c) – V = IR = 10 × 2 = 20 V (Ohm’s law application).
5. The main function of xylem in plants is
   (a) Transport of food
   (b) Transport of water
   (c) Photosynthesis
   (d) Support
   Answer: (b) – Xylem vessels conduct water/minerals upwards from roots.

6–20. Full MCQs with Answers, Reasoning & Quick Recall Tip:

6. Indicator that turns pink in basic solution: Phenolphthalein – Colourless in acid/neutral, pink in base (pH >8.2).
7. Valency of element with atomic number 16: 2 – Sulphur in S⁸, shares 2 electrons.
8. Virtual image by plane mirror: Erect, same size, laterally inverted – No convergence.
9. Commercial unit of energy: kWh (Board of Trade Unit) – 1 unit = 3.6 MJ.
10. Feedback hormone for milk ejection: Oxytocin – Posterior pituitary; uterine contraction too.
11. Variation in population: Due to sexual reproduction – Meiosis introduces recombination.
12. Acid rain caused by: SO₂ + NO₂ – Forms H₂SO₄/HNO₃, pH <5.6.
13. Vestigial organ in humans: Appendix – Reduced from herbivorous ancestors.
14. Ester functional group: –COOR – Fruity smell, from acid + alcohol.
15. Speed of sound in air: 340 m/s – At 20°C, STP.
16. Solenoid field resembles: Bar magnet – N/S poles at ends.
17. Vegetative propagation example: Potato (tubers) – Clones via stems.
18. Human evolution from: Australopithecus – Early hominid, walked upright.
19. Biodegradable waste: Cattle dung – Decomposed by bacteria.
20. Catalyst lowers: Activation energy – Speeds reaction without consumption.

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

Answer briefly; 40–60 words max per question.

Q21. Write the balanced chemical equation for the reaction between ethanol and ethanoic acid. Name the product and its use.
Answer: CH₃CH₂OH + CH₃COOH → CH₃COOCH₂CH₃ + H₂O (catalysed by H₂SO₄). Product: Ethyl ethanoate (ester); use – solvent in perfumes/nail polish remover.
Marking: 1 equation, 1 product/use. Tip: Mention catalyst for conceptual depth.

Q22. State two properties of ionic compounds. Why do they conduct electricity in molten state but not in solid?
Answer: High melting/boiling points, soluble in water. In molten/solution, ions free to move (electrolyte); solid – ions fixed in lattice.
Reasoning: Electrostatic forces strong but mobile ions conduct.

Q23. A 100 W bulb is lit for 5 hours. Calculate energy consumed in kWh.
Answer: Energy = Power × Time = 100 W × 5 h = 500 Wh = 0.5 kWh.
Step-wise: Convert to kW (0.1 kW) if needed; unit check: Wh to kWh (÷1000).

Q24. Draw a labelled diagram of the nephron and mark: glomerulus, Bowman’s capsule, collecting duct.
Answer: [Diagram: Renal artery → Glomerulus (capillary tuft in Bowman’s capsule) → Proximal tubule → Loop of Henle → Distal tubule → Collecting duct to pelvis.]
Marking: 1 diagram, 1 labels. Pro Tip: Curve the loop for realism.

Q25. Name the enzyme that digests proteins in stomach. What is its optimum pH?
Answer: Pepsin (secreted as pepsinogen); optimum pH 1.5–2 (acidic, activated by HCl).

Q26. What is adaptive radiation? Give one example.
Answer: Evolution of diverse forms from common ancestor in new habitat. Example: Darwin’s finches (beak variations for food on Galapagos).

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

Diagrams essential; show working.

Q27. A ray of light strikes a glass slab (n=1.5) at 60° incidence. Calculate angle of refraction and emergence. Draw diagram.
Answer: sin i / sin r = n → sin r = sin60° / 1.5 ≈ 0.866/1.5 = 0.577 → r ≈ 35.3°. Emergence = i = 60° (parallel slab, e = i).
[Diagram: Ray enters slab at r, refracts parallel inside, emerges at e=60°; lateral shift shown.]
Step-wise: Snell’s law; sin values from table. Marking: 1.5 calculation, 1 diagram, 0.5 nature.

Q28. Explain the role of decomposers in an ecosystem with an example. Draw a simple food web.
Answer: Decomposers (bacteria/fungi) break down dead matter, recycle nutrients (C, N cycles). Example: Fungi decompose fallen leaves → nutrients to soil → plants. Prevents waste accumulation.
[Food Web Diagram: Grass → Rabbit/Grasshopper → Frog/Snake → Eagle; Decomposers at base feeding on all dead.]
Tip: Web (interconnected) vs chain (linear).

Q29. Draw a labelled diagram of the spinal cord cross-section showing grey matter, white matter, dorsal root.
Answer: [Diagram: H-shaped grey matter (centre), white matter (outer), dorsal root (sensory, back), ventral root (motor, front), spinal nerve.]
Functions: Grey – cell bodies; white – myelinated axons.

Q30. Two cells of emf 1.5 V each connected in series with internal r=0.5 Ω each, external R=3 Ω. Find total current.
Answer: Total E = 3 V, total r = 1 Ω; I = E/(r+R) = 3/(1+3) = 0.75 A.
Step-wise: Series emf add, resistances add. Marking: 1 formula, 1 substitution, 1 answer.

Q31. What is a reflex action? Explain knee-jerk reflex with diagram.
Answer: Involuntary, rapid response to stimulus via spinal cord (bypasses brain). Knee-jerk: Tap patellar tendon → sensory to spinal → motor to quadriceps → leg kicks.
[Diagram: Spinal cord, sensory neuron from knee, interneuron, motor neuron to muscle.]

Q32. Define catenation. Why is carbon unique in this property? Give two allotropes.
Answer: Self-linking to form chains/rings. Carbon: Small size, 4 valence electrons for strong covalent bonds. Allotropes: Diamond (3D network, hard), Graphite (layers, lubricant).

Q33. Explain bio-magnification with a diagram of DDT in a food chain.
Answer: Increasing concentration of toxins up trophic levels (non-biodegradable). [Diagram: Phytoplankton (0.003 ppm DDT) → Zooplankton (0.04) → Fish (0.5) → Bird (25 ppm) – eggshells thin.] Example: DDT causes bird reproduction failure.

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

Comprehensive; use points/diagrams.

Q34. (a) Derive lens formula 1/v – 1/u = 1/f for convex lens.
(b) A lens forms image at 30 cm for object at 20 cm. Find f and power.
(c) Draw ray diagram for object between F and 2F.
Answer: (a) Derivation: For thin lens, object distance u, image v; using similar triangles from parallel ray through F, ray through O undeviated → 1/f = 1/v – 1/u (sign convention).
(b) 1/f = 1/30 – 1/(–20) = (2+3)/60 = 5/60 → f=12 cm; P=100/f=8.33 D.
[Diagram: Object between F-2F; image beyond 2F, real, inverted, magnified.]
Step-wise: Cartesian convention. Marking: 2 derivation, 2 numerical, 1 diagram.

Q35. Describe the structure and function of mitochondria with labelled diagram. Explain its role in cellular respiration.
Answer: [Diagram: Double membrane – outer smooth, inner cristae (folds); matrix inside, DNA/ribosomes.]
Structure: Powerhouse; aerobic respiration site. Function: Krebs cycle in matrix, ETC on cristae → ATP (36 from glucose). Role: Oxidative phosphorylation; 70S ribosomes for self-replication.

Q36. (Choice: (a) or (b))
(a) Explain human menstrual cycle phases with hormone roles (FSH, LH, estrogen, progesterone). Draw graph of levels.
Answer: Phases: (i) Menstrual (days 1–5: shedding, low hormones), (ii) Follicular (6–14: FSH follicle growth, estrogen thickens endometrium), (iii) Ovulation (14: LH surge, egg release), (iv) Luteal (15–28: Progesterone maintains lining; if no pregnancy, cycle restarts).
[Graph: X-axis days 1–28, Y-hormones; FSH peaks day 1/14, LH day 14, Estrogen day 12–14, Progesterone day 21–28.]
Hormones: FSH (follicle), LH (ovulation/corpus luteum), Estrogen (endometrium), Progesterone (implantation).
(b) [Alternative: Periodic table trends – atomic size, ionisation energy across period.]

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

Passage-based; justify with data.

Case 1 – Carbon Compounds (Step-by-Step 2025)
Passage: Ethanol (C₂H₅OH) burns: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. Used in beverages (denatured with methanol).
(i) Type of reaction: Combustion.
(ii) Why denatured? Prevent drinking (toxic additive).
(iii) Convert to ethene: Dehydration with conc H₂SO₄ at 170°C → C₂H₅OH → C₂H₄ + H₂O.
(iv) Test for unsaturation: Decolourises bromine water.

Case 2 – Magnetism (Sanskriti 2025)
Passage: Solenoid with 200 turns, length 20 cm, current 5 A; B = μ₀ n I (n=turns/length).
(i) n = 200/0.2 = 1000 turns/m.
(ii) B = 4π×10⁻⁷ × 1000 × 5 = 6.28 × 10⁻³ T.
(iii) Insert iron core: B increases (μ_r >1).
(iv) Field lines: Uniform inside, like bar magnet.

Case 3 – Environment (Carmel Convent 2025)
Passage: Food chain: Grass (1000 J) → Deer (100 J) → Lion (10 J); 10% energy transfer.
(i) Energy at producer: 1000 J.
(ii) Why 90% loss? Respiration, heat, undigested waste.
(iii) Pyramid shape: Decreasing energy/biomass up levels.
(iv) Impact of removing deer: Grass overgrows, lion starves.

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

Q37. Full Protocol: To show that white light splits into spectrum using glass prism.
Aim: Demonstrate dispersion. Apparatus: Prism, white light source, screen. Procedure: (1) Place prism on table. (2) Direct white light through one face. (3) Observe coloured band on screen (VIBGYOR). (4) Rotate prism for pure spectrum. Observation: Red deviates least, violet most (different wavelengths). Conclusion: Dispersion due to varying speeds in medium. Precautions: Clean prism, dark room. [Diagram: Light ray → Prism → Spectrum on screen.]

Q38. Full Protocol: To plot V-I graph for a semiconductor diode.
Aim: Show rectification. Apparatus: Diode, battery, milliammeter, voltmeter, rheostat. Procedure: (1) Connect forward bias (p to +ve). (2) Vary rheostat, note V and I. (3) Reverse connections for reverse bias. Observation Table: Forward – V=0.2V I=1mA; up to 0.7V breakdown. Reverse – negligible I till breakdown. Graph: Forward exponential, reverse flat. Conclusion: Diode conducts one way. [Graph: X-V, Y-I; forward curve, reverse line.]

Elite Exam Hacks for Unbeatable Performance (Aim 100/80)

1. Strategic Prep: Allocate 20% time to diagrams (practice 20 sketches); 30% numericals (solve 50 variants).
2. In-Exam Flow: Scan paper first (5 min); start with A (quick wins); B/C for momentum; D/E for depth.
3. Answer Polish: Bold key terms; use “hence” for conclusions; 1.5 line spacing for readability.
4. Scoring Boost: For 5-markers, 5 points = 5 marks; add “e.g.” for examples.
5. Trap Avoidance: Optics signs: Real negative; Biology: Label clockwise.
6. Case Mastery: Quote passage data in answers (e.g., “As per given, 10 J…”).
7. Practical Edge: Recall viva: “Why destarch? To ensure no prior starch.”
8. Mindset: Breathe deep if stuck (1 min); positive affirmation: “I’ve prepared – I deliver.”
9. Post-Paper: Note 3 learnings; next mock – improve by 5 marks.
10. Resources: NCERT Exemplar + Oswaal solved papers for patterns.