ADEPT YOURSELF
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CBSE CLASS X – SCIENCE SAMPLE QUESTION PAPER
SET – 6 | ACADEMIC SESSION 2026–2027
General Instructions:
- This question paper consists of 39 questions divided into Sections A, B and C.
- All questions are compulsory.
- Internal choices are provided in some questions. Attempt only one alternative wherever applicable.
- Questions include MCQs, Assertion–Reason, Very Short Answer, Short Answer, Case-Based and Long Answer questions.
- Marks are indicated against each question.
- Write all answers clearly and show necessary calculations wherever required.
- Draw neat and properly labelled diagrams wherever asked.
SECTION A – BIOLOGY
Q1.
During vigorous exercise, the accumulation of which substance in our muscle cells causes cramps?[1]
Q2.
Which part of the brain is primarily responsible for maintaining posture and the balance of the body?[1]
Q3.
In which of the following organisms does multiple fission occur as a mode of reproduction?[1]
Q4.
A cross between a tall plant (TT) and a short pea plant (tt) resulted in progeny that were all tall plants because:[1]
Q5.
Which of the following synthetic chemicals is primarily responsible for the depletion of the stratospheric ozone layer?[1]
Q6.
In a terrestrial ecosystem, what percentage of the energy of sunlight that falls on the leaves of green plants is converted into food energy?[1]
Q7.Assertion (A):
The walls of the ventricles of the human heart are thicker than those of the atria.
Reason (R): Ventricles have to pump blood into various organs of the body under high pressure.[1]
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Reason (R): Ventricles have to pump blood into various organs of the body under high pressure.[1]
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Q8.Assertion (A):
Variations arising during asexual reproduction are significantly lesser in number compared to sexual reproduction.
Reason (R): Asexual reproduction involves only DNA copying mechanisms without the fusion of gametes from two different individuals.[1]
Reason (R): Asexual reproduction involves only DNA copying mechanisms without the fusion of gametes from two different individuals.[1]
Q9.
Why is the rate of breathing in aquatic organisms much faster than that seen in terrestrial organisms?[2]
Q10.
State two differences between self-pollination and cross-pollination.[2]
Q11.(a) Name the endocrine gland associated with the kidneys.
(b) Which hormone is secreted by this gland during emergency or “fight-or-flight” situations?
(c) State two physiological responses in the human body triggered by this hormone.[3]
(b) Which hormone is secreted by this gland during emergency or “fight-or-flight” situations?
(c) State two physiological responses in the human body triggered by this hormone.[3]
Q12.
What is the Law of Segregation? Illustrate this law by showing a monohybrid cross between a homozygous round-seeded (RR) pea plant and a wrinkled-seeded (rr) pea plant up to the F₂ generation.[3]
Q13.
Explain how the human respiratory system is structurally designed to maximise the area for gaseous exchange.[3]
Q14. Read the following passage and answer the questions:[4]
(b) What role do decomposers play in an ecosystem?
(c) Suggest two practical measures you can take at an individual level to minimise waste generation.
OR
Explain why cloth or jute bags should be preferred over thin plastic bags when shopping for groceries.
Disposal of waste generated in cities and towns is a major environmental challenge. Modern lifestyles have produced large amounts of packaging materials and disposable items. Biodegradable waste can be converted into useful manure through composting. Non-biodegradable waste, especially single-use plastics, accumulates in landfills, clogs drainage systems, and pollutes water bodies, demanding systemic waste segregation and recycling policies.
(a) Differentiate between biodegradable and non-biodegradable domestic waste with one example of each.(b) What role do decomposers play in an ecosystem?
(c) Suggest two practical measures you can take at an individual level to minimise waste generation.
OR
Explain why cloth or jute bags should be preferred over thin plastic bags when shopping for groceries.
Q15.(a) Draw a neat labelled diagram of the longitudinal section of a bisexual flower showing its reproductive parts.
(b) Explain the events of pollination, pollen tube growth, and double fertilisation that lead to seed formation in flowering plants.
(c) State what the ovule and the ovary develop into after fertilisation.[5]
(b) State the primary functions of the following parts:
(i) Cerebrum (ii) Hypothalamus (iii) Medulla oblongata
(c) Differentiate between a cranial nerve and a spinal nerve.
(b) Explain the events of pollination, pollen tube growth, and double fertilisation that lead to seed formation in flowering plants.
(c) State what the ovule and the ovary develop into after fertilisation.[5]
OR
(a) Draw a labelled diagram of the human brain.(b) State the primary functions of the following parts:
(i) Cerebrum (ii) Hypothalamus (iii) Medulla oblongata
(c) Differentiate between a cranial nerve and a spinal nerve.
SECTION B – CHEMISTRY
Q16.
When clear limewater turns milky upon passing a gas through it, the precipitate formed is:[1]
Q17.
Which of the following metals does not react with either cold water, hot water, or steam?[1]
Q18.
Bleaching powder is chemically represented as:[1]
Q19.
The number of single covalent bonds present in a molecule of propane ($C_3H_8$) is:[1]
Q20.
When blue crystals of copper sulphate are heated in a dry test tube, they turn white because of:[1]
Q21.Assertion (A):
Aqueous solutions of glucose and alcohol do not conduct electricity, whereas aqueous solutions of hydrochloric acid conduct electricity.
Reason (R): Hydrochloric acid ionises in water to produce free hydrogen ions ($H^+$), whereas glucose and alcohol do not dissociate into ions.[1]
Reason (R): Hydrochloric acid ionises in water to produce free hydrogen ions ($H^+$), whereas glucose and alcohol do not dissociate into ions.[1]
Q22.
Why is respiration considered an exothermic reaction? Write the overall balanced chemical equation representing cellular respiration.[2]
Q23.
What is an electrolytic refining process? Explain the refining of blister copper with a neat schematic diagram or description, stating what is used as the anode, cathode, and electrolyte.[3]
(b) Show the formation of sodium chloride (NaCl) by electron transfer.
(c) Explain why sodium chloride conducts electricity in the molten state but not in the solid crystal state.
OR
(a) Write electron dot structures for sodium (Na, atomic number 11) and chlorine (Cl, atomic number 17).(b) Show the formation of sodium chloride (NaCl) by electron transfer.
(c) Explain why sodium chloride conducts electricity in the molten state but not in the solid crystal state.
Q24.(a) What are structural isomers?
(b) Draw the structural formulas and write the IUPAC names for the two structural isomers of butane ($C_4H_{10}$).[3]
(b) Draw the structural formulas and write the IUPAC names for the two structural isomers of butane ($C_4H_{10}$).[3]
Q25. Read the following passage and answer the questions:[4]
(b) Write the balanced chemical equation for the displacement reaction occurring between iron and aqueous copper sulphate.
(c) Can copper metal displace zinc from zinc sulphate solution? Justify your answer based on the reactivity series.
OR
Explain the thermite reaction. Write its balanced chemical equation and mention one practical industrial application.
Metals exhibit distinct reactivities when interacting with air, water, and acids. Arranging metals in the descending order of their chemical reactivities gives the reactivity series. Metals placed above hydrogen can displace hydrogen gas from dilute mineral acids, whereas metals placed below hydrogen cannot. A more reactive metal displaces a less reactive metal from its salt solution, which is used in metallurgy and displacement reactions.
(a) What will happen if an iron nail is dipped into a blue copper sulphate solution? State the observation.(b) Write the balanced chemical equation for the displacement reaction occurring between iron and aqueous copper sulphate.
(c) Can copper metal displace zinc from zinc sulphate solution? Justify your answer based on the reactivity series.
OR
Explain the thermite reaction. Write its balanced chemical equation and mention one practical industrial application.
Q26.(a) What happens when ethanol is heated with concentrated sulphuric acid at 443 K? Name the reaction and write the balanced chemical equation.
(b) How can you distinguish experimentally between an alcohol (ethanol) and a carboxylic acid (ethanoic acid) using sodium hydrogen carbonate?
(c) Write the chemical equation for the oxidation of ethanol to ethanoic acid using alkaline potassium permanganate ($KMnO_4$).[5]
(b) How is Plaster of Paris obtained from gypsum? Write the balanced chemical equation with temperature conditions.
(c) Why should Plaster of Paris always be stored in a moisture-proof container?
(d) Give two commercial applications of Plaster of Paris.
(b) How can you distinguish experimentally between an alcohol (ethanol) and a carboxylic acid (ethanoic acid) using sodium hydrogen carbonate?
(c) Write the chemical equation for the oxidation of ethanol to ethanoic acid using alkaline potassium permanganate ($KMnO_4$).[5]
OR
(a) Define water of crystallisation. Give two examples of hydrated salts with their chemical formulas.(b) How is Plaster of Paris obtained from gypsum? Write the balanced chemical equation with temperature conditions.
(c) Why should Plaster of Paris always be stored in a moisture-proof container?
(d) Give two commercial applications of Plaster of Paris.
Q27.
Identify the type of chemical reaction in each of the following:
(a) Quicklime reacts vigorously with water to form slaked lime, releasing a large amount of heat.
(b) Silver chloride turns grey when exposed to sunlight.[2]
(a) Quicklime reacts vigorously with water to form slaked lime, releasing a large amount of heat.
(b) Silver chloride turns grey when exposed to sunlight.[2]
SECTION C – PHYSICS
Q28.
The focal length of a concave mirror having a radius of curvature of 30 cm is:[1]
Q29.
The split-ring (commutator) in an electric motor acts to:[1]
Q30.
If the diameter of a uniform metallic wire of resistance R is doubled while keeping its length unchanged, its new resistance will be:[1]
Q31.
Which optical phenomenon is primarily responsible for the twinkling of stars in the night sky?[1]
Q32.Assertion (A):
A fuse wire must always be connected in the live wire of an electrical circuit.
Reason (R): If the fuse melts in the live wire during an overload, the appliance is completely isolated from the high voltage supply.[1]
Reason (R): If the fuse melts in the live wire during an overload, the appliance is completely isolated from the high voltage supply.[1]
Q33.Assertion (A):
A convex mirror is preferred as a driver’s rear-view mirror because it always gives an erect image and provides a wider field of view.
Reason (R): A convex mirror always forms a virtual, erect, and magnified image of an object regardless of its position.[1]
Reason (R): A convex mirror always forms a virtual, erect, and magnified image of an object regardless of its position.[1]
Q34.
An electric lamp of resistance 20 Ω and a conductor of resistance 4 Ω are connected in series to a 6 V battery. Calculate:
(a) The total resistance of the circuit.
(b) The current flowing through the circuit.[2]
(a) The total resistance of the circuit.
(b) The current flowing through the circuit.[2]
Q35.
Define refractive index of a medium. Write the mathematical relation between the refractive index of a medium and the speed of light in vacuum.[2]
OR
The absolute refractive index of diamond is 2.42. What does this statement mean with respect to the speed of light?Q36.(a) What is hypermetropia (farsightedness)? State its two main causes.
(b) Name the type of lens used to correct hypermetropia.
(c) Draw a ray diagram showing the correction of a hypermetropic eye using a suitable lens.[3]
(b) Name the type of lens used to correct hypermetropia.
(c) Draw a ray diagram showing the correction of a hypermetropic eye using a suitable lens.[3]
Q37.
State Fleming’s Left-Hand Rule. On what principle does an electric motor work?[3]
Q38. Read the following passage and answer the questions:[4]
(b) Where should an object be placed in front of a convex lens to obtain a real image of the same size as the object?
(c) A concave lens has a focal length of 15 cm. At what distance should an object be placed from the lens so that it forms an image 10 cm from the lens?
OR
An object 5 cm high is placed at a distance of 20 cm from a convex lens of focal length 10 cm. Find the nature, position, and height of the image formed.
Refraction through spherical lenses produces real or virtual images depending on object distance. A converging (convex) lens bends light inwards, while a diverging (concave) lens spreads light rays apart. The relationship between object distance ($u$), image distance ($v$), and focal length ($f$) is expressed by the lens formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u}$. The magnification produced by a lens is given by $m = \frac{v}{u} = \frac{h_i}{h_o}$.
(a) What is the sign of focal length for a concave lens according to the New Cartesian Sign Convention?(b) Where should an object be placed in front of a convex lens to obtain a real image of the same size as the object?
(c) A concave lens has a focal length of 15 cm. At what distance should an object be placed from the lens so that it forms an image 10 cm from the lens?
OR
An object 5 cm high is placed at a distance of 20 cm from a convex lens of focal length 10 cm. Find the nature, position, and height of the image formed.
Q39.(a) State Ohm’s law and write its mathematical formula.
(b) Derive the formula for the equivalent resistance ($R_s$) of three resistors $R_1$, $R_2$, and $R_3$ connected in series.
(c) An electric iron consumes energy at a rate of 840 W when heating is at maximum and 360 W when heating is at minimum. The voltage is 220 V. Calculate the current and the resistance in each case.[5]
(b) How does a solenoid behave like a bar magnet? State one method to determine its magnetic polarity.
(c) What is an electromagnet? Mention two ways by which the strength of an electromagnet can be increased.
(b) Derive the formula for the equivalent resistance ($R_s$) of three resistors $R_1$, $R_2$, and $R_3$ connected in series.
(c) An electric iron consumes energy at a rate of 840 W when heating is at maximum and 360 W when heating is at minimum. The voltage is 220 V. Calculate the current and the resistance in each case.[5]
OR
(a) What is a solenoid? Describe the magnetic field pattern inside and around a current-carrying solenoid.(b) How does a solenoid behave like a bar magnet? State one method to determine its magnetic polarity.
(c) What is an electromagnet? Mention two ways by which the strength of an electromagnet can be increased.
CBSE CLASS X SCIENCE – COMPLETE SOLUTIONS & MARKING SCHEME (SET – 6)
SECTION A – BIOLOGY SOLUTIONS
Q1. (c) Lactic acid [1 Mark]
Explanation: When there is a lack of oxygen in our muscle cells during vigorous physical activity, pyruvate is converted into lactic acid (a 3-carbon molecule). The buildup of lactic acid causes fatigue and muscle cramps.
Explanation: When there is a lack of oxygen in our muscle cells during vigorous physical activity, pyruvate is converted into lactic acid (a 3-carbon molecule). The buildup of lactic acid causes fatigue and muscle cramps.
Q2. (b) Cerebellum [1 Mark]
Explanation: The cerebellum, located in the hindbrain, is responsible for precision of voluntary actions and maintaining posture, equilibrium, and body balance.
Explanation: The cerebellum, located in the hindbrain, is responsible for precision of voluntary actions and maintaining posture, equilibrium, and body balance.
Q3. (b) Plasmodium [1 Mark]
Explanation: The malarial parasite Plasmodium divides into many daughter cells simultaneously inside a cyst through the process of multiple fission.
Explanation: The malarial parasite Plasmodium divides into many daughter cells simultaneously inside a cyst through the process of multiple fission.
Q4. (a) Tallness is the dominant trait [1 Mark]
Explanation: In a monohybrid cross, only the dominant trait (tallness, represented by allele ‘T’) is phenotypically expressed in the heterozygous F₁ generation (Tt), masking the recessive trait (shortness, ‘t’).
Explanation: In a monohybrid cross, only the dominant trait (tallness, represented by allele ‘T’) is phenotypically expressed in the heterozygous F₁ generation (Tt), masking the recessive trait (shortness, ‘t’).
Q5. (a) Chlorofluorocarbons (CFCs) [1 Mark]
Explanation: Synthetic chemicals like chlorofluorocarbons (CFCs), widely used as refrigerants and in fire extinguishers, release chlorine free radicals in the stratosphere which catalytically break down ozone ($O_3$) molecules into oxygen ($O_2$).
Explanation: Synthetic chemicals like chlorofluorocarbons (CFCs), widely used as refrigerants and in fire extinguishers, release chlorine free radicals in the stratosphere which catalytically break down ozone ($O_3$) molecules into oxygen ($O_2$).
Q6. (b) About 1% [1 Mark]
Explanation: Terrestrial green plants capture only about 1% of the solar energy falling on their leaves and convert it into chemical food energy via photosynthesis.
Explanation: Terrestrial green plants capture only about 1% of the solar energy falling on their leaves and convert it into chemical food energy via photosynthesis.
Q7. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: The atria receive blood at low pressure and push it down into the adjacent ventricles. Ventricles must force blood out into distant parts of the body (lungs and systemic circulation) through extensive vascular networks under high systolic pressure, requiring thicker muscular walls.
Explanation: The atria receive blood at low pressure and push it down into the adjacent ventricles. Ventricles must force blood out into distant parts of the body (lungs and systemic circulation) through extensive vascular networks under high systolic pressure, requiring thicker muscular walls.
Q8. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Asexual reproduction involves only mitotic divisions and accurate DNA replication with minor biochemical inaccuracies, producing near-identical clones. In contrast, sexual reproduction involves meiosis, crossing over, and fusion of different parental gametes, resulting in substantial genetic variations.
Explanation: Asexual reproduction involves only mitotic divisions and accurate DNA replication with minor biochemical inaccuracies, producing near-identical clones. In contrast, sexual reproduction involves meiosis, crossing over, and fusion of different parental gametes, resulting in substantial genetic variations.
Q9. Rate of Breathing in Aquatic Organisms: [2 Marks]
- Aquatic organisms obtain oxygen dissolved in water, whereas terrestrial organisms use atmospheric oxygen. [1 Mark]
- Because the concentration of dissolved oxygen in water is relatively very low compared to the concentration of oxygen in air (~21%), aquatic animals must breathe much faster to extract sufficient oxygen for cellular respiration. [1 Mark]
Q10. Self-Pollination vs Cross-Pollination: [2 Marks]
| Feature | Self-Pollination | Cross-Pollination |
|---|---|---|
| Definition | Transfer of pollen grains from anther to stigma of the same flower or another flower on the same plant. | Transfer of pollen grains from anther of one flower to stigma of another flower on a different plant of the same species. |
| External Agents | Does not usually require external pollinating agents. | Requires external pollinating agents such as wind, insects, or water. |
Q11. Adrenal Gland and Adrenaline: [3 Marks]
- (a) Adrenal gland (located on top of both kidneys). [0.5 Mark]
- (b) Adrenaline (or epinephrine). [0.5 Mark]
- (c) Physiological responses:
- Heart beats faster, increasing blood and oxygen delivery to skeletal muscles. [1 Mark]
- Breathing rate increases due to rapid contractions of the diaphragm and rib muscles; blood supply to the digestive system and skin is reduced due to vasoconstriction. [1 Mark]
Q12. Law of Segregation & Monohybrid Cross: [3 Marks]
- Law of Segregation: Alleles for a trait separate (segregate) during gamete formation so that each gamete carries only one allele for each gene. [1 Mark]
- Cross:
- Parents: Round (RR) $\times$ Wrinkled (rr) $\rightarrow$ Gametes: R and r
- F₁ Generation: Rr (All Round seeds) [0.5 Mark]
- Selfing F₁ ($\text{Rr} \times \text{Rr}$): Gametes: R, r and R, r
- Punnett Square:
• RR (Homozygous Round): 1
• Rr (Heterozygous Round): 2
• rr (Homozygous Wrinkled): 1 [1 Mark] - F₂ Phenotypic Ratio: 3 Round : 1 Wrinkled. [0.5 Mark]
Q13. Structural Design of Human Lungs for Gaseous Exchange: [3 Marks]
- Extensive Branching: Inside the lungs, the primary bronchi branch repeatedly into secondary and tertiary bronchioles, ending in balloon-like structures called alveoli. [1 Mark]
- Enormous Surface Area: The millions of alveoli present in both lungs provide a vast surface area (approx. 80 m² if unrolled) that maximises the rate of gas diffusion. [1 Mark]
- Thin Walls & Rich Capillary Network: The alveolar walls are extremely thin (one-cell thick) and surrounded by an extensive network of blood capillaries, facilitating fast and efficient exchange of $O_2$ and $CO_2$. [1 Mark]
Q14. Case-Based Solutions (Biology): [4 Marks]
- (a) Biodegradable waste: Can be decomposed into natural harmless substances by microbes (e.g., fruit peels, paper). Non-biodegradable waste: Cannot be broken down by biological processes and persists in the environment (e.g., plastic bottles, polythene bags). [1 Mark]
- (b) Decomposers break down complex organic remains of dead plants and animals into simpler inorganic nutrients that return to the soil and air, recycling matter and maintaining soil fertility. [1 Mark]
- (c) Individual measures: (i) Segregate wet organic waste from dry recyclable waste at home; (ii) Carry reusable cloth/jute bags and avoid single-use plastic articles. [2 Marks]
- Cloth and jute bags are made from renewable natural plant fibres, are fully biodegradable, and can be reused dozens of times without causing environmental pollution. In contrast, thin plastic bags are non-biodegradable, release toxic fumes when burned, choke terrestrial wildlife and marine life, and persist in landfills for centuries. [2 Marks]
Q15. Long Answer (Biology): [5 Marks]
- (a) Flower Diagram: Neat labelled diagram showing Petal, Sepal, Stamen (Anther + Filament), and Pistil/Carpel (Stigma, Style, Ovary, Ovule). [2 Marks]
- (b) Process of Fertilisation:
- Pollination: Pollen grains land on the sticky surface of the receptive stigma. [0.5 Mark]
- Pollen tube growth: A pollen tube emerges from the pollen grain, travels down through the style, and enters the ovule inside the ovary. [0.5 Mark]
- Fertilisation: The male gamete travels down the tube and fuses with the female egg cell inside the ovule to form a diploid zygote. [1 Mark]
- (c) Post-fertilisation development: The ovule develops into a tough-coated seed, and the ovary ripens and grows into the fruit. [1 Mark]
- (a) Brain Diagram: Neat diagram labelling Forebrain (Cerebrum), Midbrain, Hindbrain (Pons, Medulla, Cerebellum), Meninges, and Cranium/Skull. [2 Marks]
- (b) Functions:
- Cerebrum: Main thinking and sensory processing centre; controls intelligence, voluntary muscle movements, memory, and reasoning. [1 Mark]
- Hypothalamus: Regulates body temperature, hunger, thirst, sleep-wake cycles, and controls pituitary hormone secretions. [0.5 Mark]
- Medulla oblongata: Controls vital involuntary autonomic reflexes like heartbeat, blood pressure, peristalsis, and vomiting. [0.5 Mark]
- (c) Cranial nerves: Arise directly from the brain (12 pairs in humans). Spinal nerves: Arise from the spinal cord along the vertebral column (31 pairs in humans). [1 Mark]
SECTION B – CHEMISTRY SOLUTIONS
Q16. (b) Calcium carbonate [1 Mark]
Explanation: Passing carbon dioxide gas through limewater produces an insoluble white precipitate of calcium carbonate: $Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s)\downarrow + H_2O(l)$.
Explanation: Passing carbon dioxide gas through limewater produces an insoluble white precipitate of calcium carbonate: $Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s)\downarrow + H_2O(l)$.
Q17. (d) Copper [1 Mark]
Explanation: Copper is placed below hydrogen in the metal reactivity series and does not react with cold water, hot water, or steam.
Explanation: Copper is placed below hydrogen in the metal reactivity series and does not react with cold water, hot water, or steam.
Q18. (b) CaOCl₂ [1 Mark]
Explanation: Bleaching powder is calcium oxychloride, with chemical formula $CaOCl_2$, prepared by passing dry chlorine gas over dry slaked lime: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$.
Explanation: Bleaching powder is calcium oxychloride, with chemical formula $CaOCl_2$, prepared by passing dry chlorine gas over dry slaked lime: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$.
Q19. (b) 10 [1 Mark]
Explanation: Propane has the molecular formula $C_3H_8$. Its structural formula contains 2 carbon-carbon ($C-C$) single bonds and 8 carbon-hydrogen ($C-H$) single bonds, giving a total of $2 + 8 = 10$ single covalent bonds.
Explanation: Propane has the molecular formula $C_3H_8$. Its structural formula contains 2 carbon-carbon ($C-C$) single bonds and 8 carbon-hydrogen ($C-H$) single bonds, giving a total of $2 + 8 = 10$ single covalent bonds.
Q20. (a) Loss of water of crystallisation [1 Mark]
Explanation: Blue hydrated copper sulphate crystals contain 5 molecules of water of crystallisation ($CuSO_4 \cdot 5H_2O$). On heating, this water evaporates, leaving behind anhydrous, white $CuSO_4$.
Explanation: Blue hydrated copper sulphate crystals contain 5 molecules of water of crystallisation ($CuSO_4 \cdot 5H_2O$). On heating, this water evaporates, leaving behind anhydrous, white $CuSO_4$.
Q21. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Electrical conductivity in aqueous solutions requires mobile ions. HCl dissociates into $H^+(aq)$ and $Cl^-(aq)$ ions to carry current, whereas covalent molecules like glucose ($C_6H_{12}O_6$) and ethanol do not form ions in water.
Explanation: Electrical conductivity in aqueous solutions requires mobile ions. HCl dissociates into $H^+(aq)$ and $Cl^-(aq)$ ions to carry current, whereas covalent molecules like glucose ($C_6H_{12}O_6$) and ethanol do not form ions in water.
Q22. Exothermic Nature of Respiration: [2 Marks]
- Respiration is considered exothermic because during this biochemical process, glucose combines with oxygen in cells and breaks down into carbon dioxide and water, releasing a significant amount of energy in the form of ATP. [1 Mark]
- Chemical Equation: $C_6H_{12}O_6(aq) + 6O_2(aq) \rightarrow 6CO_2(aq) + 6H_2O(l) + \text{Energy (ATP)}$ [1 Mark]
Q23. Electrolytic Refining of Copper: [3 Marks]
- Setup:
- Anode (+): A thick block of impure (blister) copper. [0.5 Mark]
- Cathode (–): A thin strip of pure copper metal. [0.5 Mark]
- Electrolyte: Acidified copper sulphate solution ($CuSO_4 + \text{dil. } H_2SO_4$). [0.5 Mark]
- Working: When electric current is passed through the electrolyte, pure copper from the anode dissolves into the solution, and an equivalent amount of pure copper from the solution is deposited onto the cathode. [1 Mark]
- Insoluble impurities settle down at the bottom of the anode as anode mud. [0.5 Mark]
- (a) Electron Dot Structures:
- Sodium: $Na \cdot$ (electronic configuration 2, 8, 1) [0.5 Mark]
- Chlorine: $:\ddot{\text{Cl}}\cdot$ (electronic configuration 2, 8, 7) [0.5 Mark]
- (b) Transfer: $Na \rightarrow Na^+ + e^-$; $\text{Cl} + e^- \rightarrow Cl^-$; $Na^+ + Cl^- \rightarrow NaCl$. [1 Mark]
- (c) In solid NaCl, ions are held rigidly in fixed lattice positions by strong electrostatic forces and cannot move. In the molten or aqueous state, these ionic bonds break due to thermal energy/hydration, allowing free ions to move and conduct electricity. [1 Mark]
Q24. Isomers of Butane: [3 Marks]
- (a) Structural Isomers: Compounds having identical molecular formulas but different structural arrangements of atoms in their molecules. [1 Mark]
- (b) Two isomers of butane ($C_4H_{10}$):
- n-Butane (Butane): $CH_3-CH_2-CH_2-CH_3$ [1 Mark]
- Isobutane (2-Methylpropane): $CH_3-CH(CH_3)-CH_3$ [1 Mark]
Q25. Case-Based Solutions (Chemistry): [4 Marks]
- (a) The blue colour of the copper sulphate solution gradually fades to light green, and a reddish-brown coating of copper metal is deposited on the surface of the iron nail. [1 Mark]
- (b) Equation: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$ [1 Mark]
- (c) No, copper cannot displace zinc from zinc sulphate solution because copper lies below zinc in the reactivity series and is less reactive than zinc. [2 Marks]
- The reaction of iron(III) oxide with aluminium powder is highly exothermic, producing molten iron used to weld broken railway tracks and cracked machine parts. [1 Mark]
- Chemical Equation: $Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat}$ [1 Mark]
Q26. Long Answer (Chemistry): [5 Marks]
- (a) Dehydration of Ethanol: Heating ethanol with conc. $H_2SO_4$ at 443 K removes a molecule of water to yield ethene. It is an acidic dehydration reaction.
$CH_3CH_2OH \xrightarrow{\text{conc. } H_2SO_4, 443\text{ K}} CH_2=CH_2 + H_2O$ [2 Marks] - (b) Chemical Test: Add sodium hydrogen carbonate ($NaHCO_3$) to both compounds:
- Ethanoic acid reacts vigorously with brisk effervescence due to the evolution of $CO_2$ gas: $CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2\uparrow$.
- Ethanol does not react with $NaHCO_3$, showing no effervescence. [1.5 Marks]
- (c) Oxidation Equation: $CH_3CH_2OH + 2[O] \xrightarrow{\text{alkaline } KMnO_4 + \Delta} CH_3COOH + H_2O$ [1.5 Marks]
- (a) Water of Crystallisation: The fixed number of water molecules chemically bonded within one formula unit of a crystalline salt.
Examples: Washing soda ($Na_2CO_3 \cdot 10H_2O$) and Gypsum ($CaSO_4 \cdot 2H_2O$). [1.5 Marks] - (b) Preparation of POP: Heated at carefully controlled 373 K (100°C):
$CaSO_4 \cdot 2H_2O \xrightarrow{373\text{ K}} CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O$ [1.5 Marks] - (c) POP absorbs moisture from the air and sets into a hard solid mass of gypsum, losing its setting properties. [1 Mark]
- (d) Uses: (i) Setting fractured bones in orthopaedics; (ii) Making decorative casts, statues, and false ceilings. [1 Mark]
Q27. Types of Chemical Reactions: [2 Marks]
- (a) $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$ $\rightarrow$ Combination reaction (and Exothermic reaction). [1 Mark]
- (b) $2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$ $\rightarrow$ Photolytic decomposition reaction. [1 Mark]
SECTION C – PHYSICS SOLUTIONS
Q28. (d) -15 cm [1 Mark]
Explanation: Focal length $f = \frac{R}{2} = \frac{-30\text{ cm}}{2} = -15\text{ cm}$ (for a concave mirror, the centre of curvature and focus lie in front of the reflecting surface, hence negative).
Explanation: Focal length $f = \frac{R}{2} = \frac{-30\text{ cm}}{2} = -15\text{ cm}$ (for a concave mirror, the centre of curvature and focus lie in front of the reflecting surface, hence negative).
Q29. (a) Reverse the direction of current in the coil every half rotation [1 Mark]
Explanation: The split-ring commutator reverses the direction of current flowing through the armature coil every half rotation, ensuring unidirectional continuous torque.
Explanation: The split-ring commutator reverses the direction of current flowing through the armature coil every half rotation, ensuring unidirectional continuous torque.
Q30. (d) R / 4 [1 Mark]
Explanation: $R = \rho \frac{l}{A} = \rho \frac{l}{\pi (d/2)^2} = \frac{4\rho l}{\pi d^2}$. When diameter $d$ is doubled to $2d$, new resistance $R’ = \frac{4\rho l}{\pi (2d)^2} = \frac{R}{4}$.
Explanation: $R = \rho \frac{l}{A} = \rho \frac{l}{\pi (d/2)^2} = \frac{4\rho l}{\pi d^2}$. When diameter $d$ is doubled to $2d$, new resistance $R’ = \frac{4\rho l}{\pi (2d)^2} = \frac{R}{4}$.
Q31. (b) Atmospheric refraction of starlight [1 Mark]
Explanation: Starlight undergoes continuous refraction through layers of air with varying optical densities and temperatures before reaching the eye, causing its apparent position and brightness to fluctuate rapidly.
Explanation: Starlight undergoes continuous refraction through layers of air with varying optical densities and temperatures before reaching the eye, causing its apparent position and brightness to fluctuate rapidly.
Q32. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Connecting the fuse into the live wire ensures that whenever excessive current blows the fuse, the electric supply to the appliance is immediately cut off from the live 220 V line, eliminating shock hazard.
Explanation: Connecting the fuse into the live wire ensures that whenever excessive current blows the fuse, the electric supply to the appliance is immediately cut off from the live 220 V line, eliminating shock hazard.
Q33. (c) A is true but R is false. [1 Mark]
Explanation: Convex mirrors always form virtual, erect, and diminished (not magnified) images of objects, allowing them to cover a wider field of view.
Explanation: Convex mirrors always form virtual, erect, and diminished (not magnified) images of objects, allowing them to cover a wider field of view.
Q34. Series Circuit Calculation: [2 Marks]
- (a) Resistors are in series: $R_{\text{total}} = R_1 + R_2 = 20\ \Omega + 4\ \Omega = \mathbf{24\ \Omega}$. [1 Mark]
- (b) Total current by Ohm’s law: $I = \frac{V}{R_{\text{total}}} = \frac{6\text{ V}}{24\ \Omega} = \mathbf{0.25\text{ A}}$. [1 Mark]
Q35. Refractive Index: [2 Marks]
- Definition: The absolute refractive index ($n$) of a transparent medium is the ratio of the speed of light in vacuum ($c$) to the speed of light in that medium ($v$). [1 Mark]
- Formula: $n = \frac{c}{v}$ [1 Mark]
- Refractive index of diamond $n = 2.42$ means that the speed of light in diamond is $\frac{1}{2.42}$ times (or about 41.3%) of its speed in vacuum ($3 \times 10^8\text{ m/s}$). [2 Marks]
Q36. Hypermetropia & Correction: [3 Marks]
- (a) Hypermetropia (Far-sightedness): A defect where a person can see distant objects clearly but cannot see nearby objects distinctly.
Causes: (i) Focal length of the eye lens is too long; (ii) Eyeball has become too short. [1.5 Marks] - (b) Corrective lens: Convex lens (converging lens) of appropriate focal length. [0.5 Mark]
- (c) Ray Diagram: Diagram showing light rays from near point $N’$ being converged by a convex lens placed in front of the eye so that they focus precisely on the retina. [1 Mark]
Q37. Fleming’s Left-Hand Rule & Motor Principle: [3 Marks]
- Rule: Stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of current, then the thumb points in the direction of motion or mechanical force acting on the conductor. [2 Marks]
- Motor Principle: A current-carrying coil placed perpendicular to a magnetic field experiences a mechanical torque that causes it to rotate continuously. [1 Mark]
Q38. Case-Based Solutions (Physics): [4 Marks]
- (a) Negative (focal length of a concave lens is always negative). [1 Mark]
- (b) At twice the focal length, i.e., at $2F_1$ (Centre of Curvature). [1 Mark]
- (c) Concave Lens Calculation:
Given: $f = -15\text{ cm}$, $v = -10\text{ cm}$ (virtual image).
Lens formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{u} = \frac{1}{v} – \frac{1}{f}$
$\frac{1}{u} = \frac{1}{-10} – \frac{1}{-15} = -\frac{1}{10} + \frac{1}{15} = \frac{-3 + 2}{30} = -\frac{1}{30}$
$\implies u = \mathbf{-30\text{ cm}}$. (The object should be placed at 30 cm in front of the lens). [2 Marks]
- Given: $h_o = +5\text{ cm}$, $u = -20\text{ cm}$, $f = +10\text{ cm}$.
$\frac{1}{v} = \frac{1}{f} + \frac{1}{u} = \frac{1}{10} + \frac{1}{-20} = \frac{2 – 1}{20} = \frac{1}{20} \implies v = \mathbf{+20\text{ cm}}$.
Magnification: $m = \frac{v}{u} = \frac{+20}{-20} = -1$.
Height of image: $h_i = m \times h_o = -1 \times 5\text{ cm} = \mathbf{-5\text{ cm}}$.
Nature: Real, inverted, same size as object, formed at $20\text{ cm}$ on the other side of the lens (at $2F_2$). [2 Marks]
Q39. Long Answer (Physics): [5 Marks]
- (a) Ohm’s Law: The electric current ($I$) flowing through a metallic conductor is directly proportional to the potential difference ($V$) across its ends, provided physical conditions like temperature remain constant: $V = I R$. [1 Mark]
- (b) Series Derivation:
In series combination, the same current $I$ flows through each resistor.
Total potential difference: $V = V_1 + V_2 + V_3$.
Applying Ohm’s law: $V_1 = I R_1$, $V_2 = I R_2$, $V_3 = I R_3$, and $V = I R_s$.
$I R_s = I R_1 + I R_2 + I R_3 \implies \mathbf{R_s = R_1 + R_2 + R_3}$. [2 Marks] - (c) Calculations:
- Maximum heating ($P = 840\text{ W}$):
$I_1 = \frac{P_1}{V} = \frac{840\text{ W}}{220\text{ V}} \approx \mathbf{3.82\text{ A}}$
$R_1 = \frac{V}{I_1} = \frac{220\text{ V}}{3.82\text{ A}} \approx \mathbf{57.60\ \Omega}$ [1 Mark] - Minimum heating ($P = 360\text{ W}$):
$I_2 = \frac{P_2}{V} = \frac{360\text{ W}}{220\text{ V}} \approx \mathbf{1.64\text{ A}}$
$R_2 = \frac{V}{I_2} = \frac{220\text{ V}}{1.64\text{ A}} \approx \mathbf{134.15\ \Omega}$ [1 Mark]
- Maximum heating ($P = 840\text{ W}$):
- (a) Solenoid: A long cylindrical coil containing a large number of close turns of insulated copper wire.
Field Pattern: Inside the solenoid, the magnetic field lines are uniform, parallel straight lines along the axis; outside, they resemble the magnetic field pattern of a bar magnet emerging from the north pole and entering the south pole. [2 Marks] - (b) One end of the current-carrying solenoid behaves as a magnetic north pole and the other as a south pole. The polarity can be determined using a magnetic compass needle or the Clock Face Rule (clockwise current = South pole; anti-clockwise current = North pole). [1.5 Marks]
- (c) Electromagnet: A temporary magnet formed by placing a soft iron core inside a current-carrying solenoid.
Ways to increase strength: (i) Increasing the magnitude of current flowing through the coil; (ii) Increasing the number of turns per unit length in the solenoid. [1.5 Marks]