⭐ SECTION – A (Questions 1 to 16)
This document contains the Preboard Science Question paper solution 2025-26 for your reference.
1. Question:
A growing plant is kept in a dark room. Only a small window was kept open near it for a few days. The top part of the plant bends towards the window. This is an example of-
(a) Chemotropism
(b) Hydrotropism
(c) Phototropism
(d) Geotropism
Answer: (c) Phototropism
Explanation: The bending of a plant shoot towards a light source is called phototropism.
2. Question:
Which of the following part of the brain helps in maintaining posture and balance of human body?
(a) Cerebellum
(b) Cerebrum
(c) Medulla
(d) Pons
Answer: (a) Cerebellum
Explanation: The cerebellum is responsible for coordination, precision, and accurate timing of movements, including posture and balance.
3. Question:
The process of obtaining food by Amoeba is done through :
(a) Dialysis
(b) Cytokinesis
(c) Pseudopodia
(d) Amoebiasis
Answer: (c) Pseudopodia
Explanation: Amoeba uses finger-like projections called pseudopodia to engulf food particles.
4. Question:
When carrying out the starch test on a leaf, why is it important to boil the leaf in alcohol?
(a) To dissolve the waxy cuticle.
(b) To make cells more permeable to iodine solution.
(c) To remove the chlorophyll.
(d) To stop chemical reactions in the cells.
Answer: (c) To remove the chlorophyll.
Explanation: Chlorophyll’s green color masks the blue-black color change that indicates the presence of starch, so it must be removed.
5. Question:
Which of the following is the correct sequence of events during binary fission in Amoeba?
(a) Nuclear division → Cytoplasmic division → Formation of two daughter cells
(b) Cytoplasmic division → Nuclear division → Formation of two daughter cells
(c) Formation of pseudopodia → Nuclear division → Cytoplasmic division
(d) Cell wall formation → Nuclear division → Cytoplasmic division
Answer: (a) Nuclear division → Cytoplasmic division → Formation of two daughter cells
Explanation: In binary fission, the nucleus divides first (karyokinesis), followed by the division of the cytoplasm (cytokinesis).
6. Question:
Which of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest
Answer: (b) Crop field
Explanation: Crop fields are man-made and managed ecosystems, unlike forests, lakes, or ponds which are generally natural.
7. Question:
Accumulation of non biodegradable pesticides in the food chain in increasing amount at each higher tropic level is known as:
(a) Eutrophication
(b) Pollution
(c) Biomagnification
(d) Accumulation
Answer: (c) Biomagnification
8. Question:
Assertion (A) – When tall plants with dominant traits are crossed with short plants with recessive traits, all the plants in F1 progeny are tall. When the tall plants of F1 progeny are crossed, short plants reappear in F2 progeny.
Reason (R)- Traits are independently inherited.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true, and R is not the correct explanation of A.
Explanation: The reappearance of short plants in F2 (monohybrid cross) is due to the Law of Segregation, not Independent Assortment.
9. Question:
Assertion (A) – The number of trophic levels in a food chain is limited.
Reason (R) – There is a loss of energy as we go from one trophic level to the next.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true, and R is the correct explanation of A
Explanation: According to the 10% law, only 10% energy is transferred to the next level. After 3–4 levels, very little energy remains.
10. Question:
(A) Name the final product/products obtained in the anaerobic respiration, if it takes place:
(a) In a fungi (like yeast).
(b) In an animal tissue (like muscles).
OR
(B) Define excretion. Name any one method used by plants to get rid of excretory products?
Answer (A):
(a) In Yeast: Ethanol (C₂H₅OH), Carbon dioxide (CO₂), and Energy.
(b) In Muscles: Lactic acid and Energy.
Answer (B):
Excretion: The biological process of removing harmful metabolic wastes from the body.
Plant Method: Shedding of old leaves / transpiration / releasing waste into soil.
11. Question:
(A) List the role of the following in our digestive system:
(a) Hydrochloric acid
(b) Trypsin
OR
(B) Write two ways by which plants obtain Carbon dioxide. What causes the opening and closing of stomata?
Answer (A):
(a) Hydrochloric acid: Creates an acidic medium for pepsin; kills bacteria.
(b) Trypsin: Digests proteins into amino acids.
Answer (B):
CO₂ obtained by:
(1) Stomata
(2) Respiration inside plant cells
Stomatal movement: Change in turgor pressure of guard cells.
12. Question:
What is ten percent law in a food chain? Explain with an example.
Answer:
10% Law: Only 10% energy available to next trophic level.
Example: Sun (1000 J) → Plants (10 J) → Deer (1 J) → Lion (0.1 J).
13. Question:
“The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Answer:
Female = XX → always gives X
Male = XY → gives X or Y
X from father → girl
Y from father → boy
Thus, father determines sex.
14. Question:
A person walks across a room in barefoot and puts his foot on a drawing pin lying on the floor. He lets out a cry. Explain…
Answer: Reflex Arc
Flowchart:
Stimulus → Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector → Response
15. Question:
(a) Basic filtration unit?
(b) How unicellular organisms remove waste?
(c) What happens to glucose in filtrate?
OR
(d) Name two waste products.
Answer:
(a) Nephron
(b) Diffusion
(c) Reabsorbed
(d) CO₂ and Urea
16. Question:
(A) (a) Binary fission vs budding (offspring).
(b) Environmental factors influence reproduction example?
OR
(B) Vegetative reproduction & advantages; Human germ-cell differences.
Answer (A):
(a) Amoeba divides into two; parent lost. Hydra forms bud; parent remains.
(b) Example: Leishmania divides in definite orientation; algae/fungi change mode during stress.
Answer (B):
(a) Vegetative propagation advantages: early fruiting, identical traits.
(b) Sperm = small & motile; Egg = large & non-motile.
⭐ SECTION – B (Questions 17 to 29)
17. Question:
Which of the following does not involve a chemical reaction?
(a) Digestion of food in our body.
(b) Process of respiration.
(c) Burning of candle wax when heated.
(d) Melting of candle wax on heating.
Answer: (d) Melting of candle wax on heating. (Physical change).
18. Question:
Which of the following represents a combination reaction?
(a) 2NaCl → 2Na + Cl₂
(b) C + O₂ → CO₂
(c) 2H₂O → 2H₂ + O₂
(d) 2HCl → H₂ + Cl
Answer: (b) C + O₂ → CO₂ (Two reactants combine to form one product).
19. Question:
When writing a chemical equation, which element is considered when balancing a reaction?
Answer: (c) Every element present in the reaction (Law of Conservation of Mass).
20. Question:
Which of the following is a characteristic property of acids?
Answer: (b) Sour taste and ability to change the color of blue litmus paper to red.
21. Question:
When an acid reacts with a metal, the reaction typically produces:
Answer: (b) Hydrogen gas and a salt.
22. Question:
When an acid reacts with a carbonate, the main products formed are:
Answer: (b) Salt, water and Carbon dioxide.
23. Question:
Which of the following group of metals react with steam but not with cold or hot water?
Answer: (b) Al, Fe, Zn (Aluminum, Iron, Zinc).
24. Question:
Assertion (A): Carbon exhibits catenation…
Reason (R): Carbon’s small atomic size…
Answer: (a) Both A and R are true, and R is the correct explanation of A.
Explanation: The small size of the carbon atom allows the nucleus to hold the shared pair of electrons strongly, resulting in very strong bonds that enable long chains (catenation).
25. Question:
Why is Sodium kept immersed in kerosene oil?
Answer: Sodium is highly reactive. It reacts vigorously with oxygen and moisture in the air to catch fire. Kerosene cuts off contact with air and moisture.
26. Question:
(A) (a) Metal soft enough to cut with knife.
(b) Best conductor of heat/electricity.
(c) Metal displacing Silver.
OR
(B) Sodium + Chlorine reaction & bonding name.
Answer (A):
(a) Sodium (or Potassium).
(b) Silver.
(c) Copper (or Zinc/Iron).
Answer (B):
Sodium (Na) loses 1 electron to become Na⁺.
Chlorine (Cl) gains 1 electron to become Cl⁻.
The oppositely charged ions attract each other.
This is Ionic Bonding (Electrovalent bond).
27. Question:
(a) Why corrosion of iron is a serious problem?
(b) Prevention methods.
Answer:
(a) Corrosion weakens the structural integrity of iron bridges, ships, and vehicles, causing massive economic loss and safety hazards.
(b) Painting, Oiling/Greasing, Galvanization (coating with Zinc).
28. Question:
Acid + Calcium Carbonate reaction.
(a) Gas?
(b) Salt?
(c) Description? [cite: 120–122]
Answer:
(a) Carbon dioxide (CO₂).
(b) Calcium Chloride (CaCl₂).
(c) When an acid reacts with a metal carbonate, it forms salt, water, and releases carbon dioxide gas (which turns lime water milky).
29. Question:
(A) Compounds X and Y have formula C₃H₆O. Names, Structures, Functional groups.
OR
(B) Hydrocarbons definition, C₂ hydrocarbons, Saturated vs Unsaturated.
Answer (A):
X (Ketone): Propanone (CH₃–CO–CH₃). Functional group: Ketone.
Y (Aldehyde): Propanal (CH₃–CH₂–CHO). Functional group: Aldehyde.
Answer (B):
Hydrocarbons: Compounds of Carbon and Hydrogen.
Two-carbon hydrocarbons: Ethane (C₂H₆), Ethene (C₂H₄), Ethyne (C₂H₂).
Reactivity: Unsaturated hydrocarbons are more reactive due to double/triple bonds.
⭐ SECTION – C (Questions 30 to 39)
30. Question:
In which of the following a concave mirror is used?
(a) A solar cooker.
(b) A rearview mirror…
Answer: (a) A solar cooker. (It concentrates sunlight to a point).
31. Question:
The sky on the moon appears dark to an astronaut because :
Answer: (b) There is no atmosphere on the surface of the moon. (No scattering of light occurs).
32. Question:
Assertion (A) – SI unit of power is dioptre.
Reason (R) – Power of concave is positive…
Answer: (c) A is true but R is false.
Explanation: The power of a concave lens is negative, and a convex lens is positive.
33. Question:
Divergent lens, f = 20cm, h = 4cm. Image formed 10cm away. Find object distance.
Answer:
Divergent lens = Concave lens. f = -20 cm. v = -10 cm (Virtual image).
Lens Formula: 1/v – 1/u = 1/f
u = -20 cm.
Object is placed 20 cm from the lens.
34. Question:
(A) Factors affecting resistance.
OR
(B) Why metals good conductors vs glass bad?
Answer (A):
(1) Length of wire
(2) Area of cross-section (thickness)
(3) Nature of material
(4) Temperature
Answer (B):
Metals have free electrons that move to conduct current.
Glass has no free electrons.
35. Question:
(a) Fuse?
(b) Material?
(c) Connection?
Answer:
(a) A safety device that breaks the circuit if current exceeds a safe limit, preventing fire/damage.
(b) Alloy of Lead and Tin (low melting point).
(c) Connected in Series with the Live wire.
36. Question:
Myopia (Near-sightedness) > 5m.
(a) Ray diagram/Reason.
(b) Correction. [cite: 162–164]
Answer:
(a) The image of distant objects is formed in front of the retina, not on it. Caused by elongation of eyeball or excessive curvature of lens.
(b) Corrected using a Concave Lens.
37. Question:
Direction of magnetic field? [cite_start]Why lines don’t cross?
Answer:
Direction: The direction in which the north pole of a compass needle points (or tangent to the field line).
No Crossing: If they crossed, the compass would point in two directions at the same time, which is impossible.
38. Question:
Refraction activity.
(a) Term?
(b) Why bend to normal?
(c) Speed/Index relationship OR
(d) Real life example. [cite: 179–185]
Answer:
(a) Refraction.
(b) Because light slows down when entering a denser medium (water) from a rarer medium (air).
(c) n = c/v (Refractive index = Speed in air / Speed in medium).
Higher index → lower speed → more bending.
(d) Example: A pencil in a glass of water looks bent.
Significance: Shows light travels at different speeds in different media; basis for how lenses work.
39. Question:
(A) Electricity Bill & Ohm’s Law.
OR
(B) Circuit Calculation (Parallel). [cite: 186–192]
Answer (A):
Energy: Heater (1kW × 5h = 5kWh) + Fridge (0.4kW × 10h = 4kWh).
Total/day = 9 kWh.
Month (30 days): 9 × 30 = 270 Units.
Cost: 270 × 6.00 = 1620 Rupees.
Ohm’s Law: Current is directly proportional to Voltage at constant temperature (V = IR).
Answer (B):
Resistors: 10Ω, 20Ω, 30Ω in Parallel, 12V Battery
(i) Current in each:
I₁ = 12/10 = 1.2A
I₂ = 12/20 = 0.6A
I₃ = 12/30 = 0.4A
(ii) Total Resistance:
1/R = 1/10 + 1/20 + 1/30 = 11/60
R ≈ 5.45 Ω
(iii) Total Current:
1.2 + 0.6 + 0.4 = 2.2 A