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.
Total Marks: 80 | Time: 3 hours
General Instructions:
- All questions are compulsory.
- Section A: 20 MCQs (1 mark each).
- Section B: 6 questions (2 marks each).
- Section C: 7 questions (3 marks each).
- Section D: 3 questions (5 marks each).
- Section E: 3 case-based questions (4 marks each).
- Internal choice in some questions.
- Use log tables if necessary. Draw neat diagrams.
Section A – Multiple Choice Questions (20 × 1 = 20 marks)
Attempt all questions. Select the correct option.
- The chemical name of baking soda is
(a) Sodium bicarbonate (NaHCO₃)
(b) Sodium carbonate (Na₂CO₃)
(c) Sodium chloride (NaCl)
(d) Sodium hydroxide (NaOH)
Answer: (a) – Baking soda is used in baking to release CO₂ and is mildly alkaline. - Which of the following is a displacement reaction?
(a) 2H₂ + O₂ → 2H₂O
(b) Zn + CuSO₄ → ZnSO₄ + Cu
(c) CaCO₃ → CaO + CO₂
(d) 2Mg + O₂ → 2MgO
Answer: (b) – More reactive Zn displaces less reactive Cu from its salt. - The focal length of a plane mirror is
(a) Zero
(b) Positive
(c) Negative
(d) Infinity
Answer: (d) – Plane mirrors form images at infinity for parallel rays. - The resistance of a wire is inversely proportional to
(a) Length
(b) Area of cross-section
(c) Temperature
(d) Material
Answer: (b) – R = ρl/A; larger area means lower resistance. - The site of photosynthesis in a plant cell is
(a) Nucleus
(b) Mitochondria
(c) Chloroplast
(d) Vacuole
Answer: (c) – Chloroplasts contain chlorophyll for light absorption.
6–20. Remaining MCQs with Answers & Brief Reasoning:
- pH of a neutral solution: 7 – Equal H⁺ and OH⁻ ions.
- Electron configuration of Mg (atomic no. 12): 2,8,2 – K=2, L=8, M=2 shells.
- Image formed by convex lens when object at 2F: At 2F, real, inverted, same size.
- Unit of electric current: Ampere – Rate of flow of charge.
- Plant hormone for fruit ripening: Ethylene – Promotes abscission and ripening.
- Acquired trait example: Muscles from exercise – Not passed to offspring.
- Greenhouse gas: CO₂ – Traps heat in atmosphere.
- Homologous organs: Forelimbs of human and whale – Same structure, different function.
- Functional group in alcohols: –OH – Hydroxyl group.
- Speed of light in vacuum: 3 × 10⁸ m/s – Constant value.
- Fleming’s left-hand rule is for: Electric motor – Force on conductor.
- Binary fission in: Amoeba – Asexual reproduction.
- Evolution by natural selection proposed by: Darwin – Survival of fittest.
- Ozone layer protects from: UV rays – Absorbs harmful radiation.
- Catalyst in Haber process: Iron – Speeds up ammonia formation.
Section B – Very Short Answer Questions (2 marks × 6 = 12 marks)
Answer all questions briefly.
Q21. Write balanced chemical equations for the following reactions:
(i) Reaction of magnesium with dilute hydrochloric acid.
(ii) Decomposition of silver chloride in sunlight.
Answer:
(i) Mg + 2HCl → MgCl₂ + H₂↑ (Displacement; Mg displaces H₂ as it’s more reactive.)
(ii) 2AgCl → 2Ag + Cl₂ (Photochemical decomposition; used in black and white photography.)
Marking Scheme: 1 mark each for balanced equation; ½ mark for state symbols if included.
Q22. State two differences between sexual and asexual reproduction. Give one example of each.
Answer:
| Sexual Reproduction | Asexual Reproduction |
|---|---|
| Involves fusion of gametes; produces variation | No fusion; offspring identical to parent |
| Slower; needs two parents | Faster; single parent |
| Examples: Human (sexual), Binary fission in Amoeba (asexual). | |
| Student Tip: Use table format for comparisons to save time and score full marks. |
Q23. A 12 V battery is connected to a resistor of 4 Ω. Calculate the current flowing through it and the power dissipated.
Answer: I = V/R = 12/4 = 3 A; P = VI = 12 × 3 = 36 W (or I²R = 9 × 4 = 36 W).
Step-wise: Use Ohm’s law first, then power formula. Units: Ampere, Watt.
Q24. Draw a labelled diagram of the human eye and mark: cornea, iris, pupil, lens, retina.
Answer: [Diagram Description: Circular eye structure – Cornea (front curved), Iris (coloured ring), Pupil (black centre), Lens (behind iris), Retina (inner back layer). Arrows labelling each part.]
Marking: 1 mark for diagram, 1 for labels.
Q25. Define refraction of light. Give one example from daily life.
Answer: Bending of light when it passes from one medium to another due to change in speed. Example: Pencil appears bent in water glass (air to water).
Tip: Always mention “change in speed” for conceptual clarity.
Q26. Name the hormone that regulates blood sugar level. What happens if it is insufficient?
Answer: Insulin (secreted by pancreas). Insufficient → Hyperglycemia (diabetes; high blood sugar, frequent urination, thirst).
Section C – Short Answer Questions (3 marks × 7 = 21 marks)
Answer all questions with diagrams where necessary.
Q27. An object 5 cm tall is placed 20 cm from a concave mirror of focal length 15 cm. Find the position, nature and size of the image. Draw ray diagram.
Answer:
Using mirror formula: 1/v + 1/u = 1/f → 1/v = 1/15 – 1/(–20) = (4 + 3)/60 = 7/60 → v = –60/7 ≈ –8.57 cm (behind mirror, virtual).
Magnification m = –v/u = –(–8.57)/(–20) = –0.428 (erect, diminished). Image size = 5 × 0.428 ≈ 2.14 cm.
Nature: Virtual, erect, diminished.
[Ray Diagram: Object between P and F; two rays – one parallel to axis reflecting through F, one through P reflecting parallel. Image between P and F.]
Step-wise Calculation: Sign convention: u negative, f negative for concave. Marking: 1 for formula/calculation, 1 for diagram, 1 for nature/size.
Q28. Explain the structure of a neuron with a labelled diagram. Mention its function in reflex action.
Answer: [Diagram: Dendrites (branched receivers), Cell body (nucleus), Axon (long fibre), Myelin sheath (insulating), Synaptic knob (transmitter end).]
Structure: Dendrites receive impulses, axon conducts, synapse transmits via chemicals. In reflex: Sensory neuron → spinal cord → motor neuron → muscle (quick response, e.g., knee jerk).
Tip: Label 5 parts for full marks; explain pathway briefly.
Q29. Draw a labelled diagram of the male reproductive system in humans. Name the glands associated.
Answer: [Diagram: Testes (oval), Vas deferens (tube from testes), Urethra (common passage), Prostate/seminal vesicle glands (add secretions), Penis.]
Glands: Testes (testosterone/sperm), Prostate (alkaline fluid), Seminal vesicles (fructose).
Marking: 2 for diagram/labels, 1 for glands.
Q30. Three resistors of 2 Ω, 3 Ω and 6 Ω are connected in parallel to a 12 V battery. Calculate the total current drawn from the battery.
Answer: 1/R_eq = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1 → R_eq = 1 Ω.
I_total = V/R_eq = 12/1 = 12 A.
Step-wise: Reciprocal sum for parallel; currents: I1=6A, I2=4A, I3=2A (sum=12A). Tip: Show individual currents for extra credit.
Q31. What is a homologous series? Write the general formula for alkanes and give two examples.
Answer: Series of compounds with same functional group, successive members differ by –CH₂. General formula for alkanes: C_nH_{2n+2}. Examples: Methane (CH₄, n=1), Ethane (C₂H₆, n=2).
Properties: Similar chemical, gradual physical change (boiling point increases).
Q32. Explain the process of budding in Hydra with a diagram.
Answer: [Diagram: Hydra body with small bud outgrowth → developing tentacles → separation as new individual.]
Budding: Asexual; bud forms on parent body, grows, matures and detaches. In Hydra, occurs in favourable conditions; leads to clone population.
Marking: 1 for diagram, 2 for explanation.
Q33. Differentiate between biodegradable and non-biodegradable wastes with two examples each. Suggest two ways to reduce waste.
Answer:
| Biodegradable | Non-Biodegradable |
|---|---|
| Decomposed by microbes | Not decomposed |
| From natural sources | Synthetic |
| Examples: Vegetable peels, paper; Plastics, glass. | |
| Reduce: Reuse items, recycle paper/plastic. Tip: Table + methods = full marks. |
Section D – Long Answer Questions (5 marks × 3 = 15 marks)
Answer any three; internal choice where given.
Q34. (a) State Fleming’s right-hand rule. Draw diagram of electric generator.
(b) An AC generator produces 220 V at 50 Hz. If a coil has 100 turns and area 0.1 m² in magnetic field 0.5 T, calculate peak emf.**
Answer: (a) Thumb: motion, forefinger: field, middle: current (induced). [Diagram: Rectangular coil in uniform B, slip rings, axle.]
(b) ε_max = NBAω = 100 × 0.5 × 0.1 × 2π × 50 = 1570.8 V (approx. 220 V RMS = ε_max/√2).
Step-wise Derivation: ω = 2πf; full formula explanation. Marking: 2 for rule/diagram, 3 for calculation.
Q35. Describe the life cycle of a frog with labelled diagrams of tadpole and adult stages. Explain metamorphosis.
Answer: [Diagrams: Egg → Tadpole (gills, tail) → Froglet (lungs developing) → Adult frog (limbs, no tail).]
Life cycle: Eggs in water → tadpole (herbivorous, aquatic) → metamorphosis (thyroxine hormone changes gills to lungs, tail absorbs) → adult (carnivorous, amphibious). 4 stages, takes 12 weeks.
Detailed: Hormonal control by thyroid; adaptive to land.
Q36. (Choice: Attempt either (a) or (b))
(a) Explain double circulation in human heart with labelled diagram. Why is it necessary?
Answer: [Diagram: Heart with 4 chambers – RA, LA, RV, LV; arrows for deoxygenated (body→lungs) and oxygenated (lungs→body) blood.]
Double: Pulmonary (heart-lungs-heart) and systemic (heart-body-heart). Necessary: Separates O₂-rich/poor blood, efficient O₂ supply, prevents mixing (evolution from fish single circulation). 4-chambered prevents backflow via valves.
Marking: 2 for diagram, 2 for explanation, 1 for necessity.
(b) [Alternative on carbon compounds – ethanol to ethanoic acid conversion with equations.]
Section E – Case/Source-Based Questions (4 marks × 3 = 12 marks)
Read the passage and answer.
Case 1 – Acids, Bases & Salts (DPS RK Puram 2025)
A student tests unknown solutions: A turns blue litmus red, B turns red litmus blue, C no change. A + B → neutral solution.
(i) Identify A, B, C.
(ii) Write reaction of A with Zn.
(iii) Name salt formed from A + NaOH.
(iv) pH of C?
Answer: (i) A=Acid, B=Base, C=Neutral. (ii) 2HCl + Zn → ZnCl₂ + H₂. (iii) NaCl. (iv) 7.
Case 2 – Optics (Modern School 2025)
Light ray from air (n=1) to diamond (n=2.42) at 30° incidence.
(i) Calculate refraction angle.
(ii) Critical angle for diamond-air.
(iii) Why diamonds sparkle (total internal reflection).
(iv) Draw diagram.
Answer: (i) sin r = sin30°/2.42 ≈ 12.3°. (ii) sin C = 1/2.42 ≈ 24.4°. (iii) Multiple TIR inside facets.
Case 3 – Heredity (Amity 2025)
In humans, blood group A (Iᴬ), B (Iᴸ), AB (IᴬIᴸ), O (ii). Father AB marries mother O; possible child groups?
(i) Genotypes of parents.
(ii) Punnett square.
(iii) Child blood groups.
(iv) Which is universal recipient?
Answer: Father IᴬIᴸ, Mother ii. Offspring: Iᴬi (A), Iᴮi (B). AB is universal recipient.
Practical-Based Questions (Internal Choice – 3 + 3 = 6 marks)
Q37. Describe the experiment to verify laws of reflection using plane mirror.
Aim: Verify i = r. Apparatus: Mirror, pins, protractor. Procedure: (1) Fix mirror vertically. (2) Place incident pin at 30° i. (3) Place reflected pins. (4) Measure r. Table: i=30°, r=30°; i=45°, r=45°. Conclusion: i = r. Precautions: Eye level with pins. [Diagram: Mirror, incident/reflected rays.]
Q38. To find refractive index of glass slab using travelling microscope.
Aim: Measure lateral shift. Procedure: (1) Place slab on paper. (2) Pin object under slab. (3) Measure shift d for thickness t. μ = t / d sin i (approx.). Conclusion: μ ≈ 1.5. [Diagram: Microscope, slab, pins.]
Advanced Exam Strategies for 100/80 Score
- Time Management: 40 min Section A, 30 min B/C, 40 min D/E, 30 min revision.
- Diagrams: Practice 10 key ones (heart, eye, neuron, ray diagrams) – label in pencil first.
- Numericals: Write formula, substitute, calculate – 70% marks from steps.
- MCQs: Eliminate wrong options; guess if 50-50.
- Cases: Read passage twice; answer in sequence.
- Practicals: Memorize 5 experiments with diagrams – common in boards.
- Common Errors: Sign convention in optics (±), balanced equations (atoms equal), units in numericals.
- Revision: Last 15 min: Check equations, labels, calculations.
