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CBSE CLASS X – SCIENCE SAMPLE QUESTION PAPER
SET – 9 | 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 anaerobic respiration in yeast cells, pyruvate is broken down into:[1]
Q2.
Which of the following is the correct sequence of components in a typical reflex arc?[1]
Q3.
When a Planaria is cut horizontally into three pieces, each piece grows into a complete organism. This biological phenomenon is termed:[1]
Q4.
In human beings, an unfertilised egg (ovum) released from the ovary always carries:[1]
Q5.
Which chemical reaction correctly represents the formation of ozone in the upper atmosphere under the influence of UV radiation?[1]
Q6.
The major driving force responsible for the movement of water upwards in xylem vessels during the daytime is:[1]
Q7.Assertion (A):
The pancreas is classified as both an endocrine and an exocrine gland (a heterocrine gland).
Reason (R): It secretes digestive enzymes like trypsin through pancreatic ducts and hormones like insulin directly into the blood.[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): It secretes digestive enzymes like trypsin through pancreatic ducts and hormones like insulin directly into the blood.[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):
Decomposers play an indispensable role in maintaining the ecological balance of an ecosystem.
Reason (R): They convert dead complex organic matter into simple inorganic nutrients that enrich the soil.[1]
Reason (R): They convert dead complex organic matter into simple inorganic nutrients that enrich the soil.[1]
Q9.
Differentiate between autotrophic nutrition and heterotrophic nutrition with respect to source of carbon and energy. Give one example of each.[2]
Q10.
Why is sexual reproduction considered advantageous over asexual reproduction in terms of the long-term survival of a species?[2]
Q11.(a) What is tropism in plants?
(b) Describe an experimental setup to demonstrate positive phototropism and negative geotropism in a growing potted shoot.
(c) Name the plant hormone that promotes stem elongation and germination of seeds.[3]
(b) Describe an experimental setup to demonstrate positive phototropism and negative geotropism in a growing potted shoot.
(c) Name the plant hormone that promotes stem elongation and germination of seeds.[3]
Q12.
In garden peas, green pod colour ($G$) is dominant over yellow pod colour ($g$). A homozygous green pod plant ($GG$) is crossed with a yellow pod plant ($gg$).
(a) Give the genotype and phenotype of the F₁ generation.
(b) Write the Punnett square for self-pollination of the F₁ generation.
(c) State the genotypic ratio and phenotypic ratio of the F₂ generation.[3]
(a) Give the genotype and phenotype of the F₁ generation.
(b) Write the Punnett square for self-pollination of the F₁ generation.
(c) State the genotypic ratio and phenotypic ratio of the F₂ generation.[3]
Q13.
What is lymph (tissue fluid)? Explain how it is formed, and state two important functions it performs in the human circulatory system.[3]
Q14. Read the following passage and answer the questions:[4]
(b) Why are patients suffering from severe diabetes treated by administering insulin injections rather than oral pills?
(c) Explain the feedback mechanism that regulates the timing and amount of insulin released by the pancreas.
OR
Name the master gland of the human endocrine system and explain how its growth hormone affects human development.
Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream in trace amounts. The pituitary gland located at the base of the brain regulates several other endocrine organs. The thyroid gland requires dietary iodine to produce thyroxin, which regulates basal metabolic rate. The pancreas produces insulin and glucagon to maintain homeostatic blood glucose levels. When insulin production is deficient, glucose levels rise above normal, leading to diabetes.
(a) Name the hormone whose deficiency leads to diabetes mellitus and identify the gland that secretes it.(b) Why are patients suffering from severe diabetes treated by administering insulin injections rather than oral pills?
(c) Explain the feedback mechanism that regulates the timing and amount of insulin released by the pancreas.
OR
Name the master gland of the human endocrine system and explain how its growth hormone affects human development.
Q15.(a) Draw a neat, well-labelled diagram of the human alimentary canal.
(b) Explain the process of digestion that takes place in the:
(i) Stomach (ii) Small intestine
(c) What is the function of intestinal juice (succus entericus)?[5]
(b) Explain the working mechanism of the following contraceptive methods:
(i) Intrauterine Contraceptive Devices (IUCDs like Copper-T)
(ii) Oral contraceptive pills
(c) State two advantages of practising family planning.
(b) Explain the process of digestion that takes place in the:
(i) Stomach (ii) Small intestine
(c) What is the function of intestinal juice (succus entericus)?[5]
OR
(a) Describe the structure of a mature human sperm with the help of a diagram.(b) Explain the working mechanism of the following contraceptive methods:
(i) Intrauterine Contraceptive Devices (IUCDs like Copper-T)
(ii) Oral contraceptive pills
(c) State two advantages of practising family planning.
SECTION B – CHEMISTRY
Q16.
An aqueous solution of sodium acetate ($CH_3COONa$) has a pH that is:[1]
Q17.
Identify the oxidising agent in the following chemical reaction:
$$MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2$$[1]
$$MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2$$[1]
Q18.
Cinnabar is a natural sulphide ore of which of the following metals?[1]
Q19.
The IUPAC name of the organic compound having structural formula $CH_3-CH_2-COOH$ is:[1]
Q20.
When an iron nail is immersed in a copper sulphate solution, it is an example of:[1]
Q21.Assertion (A):
While diluting an acid, concentrated acid must always be added slowly to water with constant stirring, and never water to acid.
Reason (R): The dilution of a concentrated mineral acid is an extremely exothermic process; adding water to concentrated acid may cause dangerous splashing and glass breakage.[1]
Reason (R): The dilution of a concentrated mineral acid is an extremely exothermic process; adding water to concentrated acid may cause dangerous splashing and glass breakage.[1]
Q22.
What is rancidity? Name two antioxidant substances or methods used commercially to prevent oily food from becoming rancid.[2]
Q23.
Explain the extraction of zinc from zinc blende ore ($ZnS$) involving roasting followed by reduction with carbon. Write balanced chemical equations for both steps.[3]
OR
State three characteristic physical properties of ionic compounds and justify each property based on their crystal lattice structure.Q24.(a) What are homologous series of carbon compounds? Give two characteristics.
(b) Draw the electron dot structure of a cyclohexane molecule ($C_6H_{12}$).
(c) How can you distinguish chemically between an alkane and an alkene using bromine water test?[3]
(b) Draw the electron dot structure of a cyclohexane molecule ($C_6H_{12}$).
(c) How can you distinguish chemically between an alkane and an alkene using bromine water test?[3]
Q25. Read the following passage and answer the questions:[4]
(b) Name the chemical substance that can be applied to the skin to get quick relief from a bee sting. Why does it work?
(c) Explain how acid rain affects the survival of aquatic organisms in rivers and lakes.
OR
Explain how self-defence mechanisms in nettle plants and dock plants illustrate natural neutralisation in nature.
The pH of various bodily fluids and environmental systems is critical for biological function. Human blood operates within a narrow pH range of 7.35 to 7.45. When the pH of rainwater drops below 5.6 due to dissolved oxides of sulphur and nitrogen, it is called acid rain. Acid rain lowers the pH of freshwater bodies, causing death to aquatic life. Similarly, when a honeybee or nettle plant stings a person, it injects methanoic (formic) acid into the skin, producing burning pain.
(a) What is acid rain? State its defining pH value.(b) Name the chemical substance that can be applied to the skin to get quick relief from a bee sting. Why does it work?
(c) Explain how acid rain affects the survival of aquatic organisms in rivers and lakes.
OR
Explain how self-defence mechanisms in nettle plants and dock plants illustrate natural neutralisation in nature.
Q26.(a) Describe the preparation of Bleaching Powder ($CaOCl_2$) with a balanced chemical equation.
(b) How is Baking Soda manufactured by the Solvay process? Write the chemical equation involved.
(c) What happens when baking soda is heated strongly during cooking? Give the chemical equation.
(d) State two important uses of Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$).[5]
(b) Explain the cleansing action of soap with the help of a neat diagram showing micelle formation.
(c) Why do soaps form insoluble curdy precipitates (scum) when used with hard water?
(b) How is Baking Soda manufactured by the Solvay process? Write the chemical equation involved.
(c) What happens when baking soda is heated strongly during cooking? Give the chemical equation.
(d) State two important uses of Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$).[5]
OR
(a) Differentiate between soaps and synthetic detergents based on their chemical composition and behaviour in hard water.(b) Explain the cleansing action of soap with the help of a neat diagram showing micelle formation.
(c) Why do soaps form insoluble curdy precipitates (scum) when used with hard water?
Q27.
Write balanced chemical equations with state symbols for the following reactions:
(a) Thermal decomposition of solid calcium carbonate into calcium oxide and carbon dioxide gas.
(b) Reaction of red-hot iron metal with steam to form iron(II,III) oxide and hydrogen gas.[2]
(a) Thermal decomposition of solid calcium carbonate into calcium oxide and carbon dioxide gas.
(b) Reaction of red-hot iron metal with steam to form iron(II,III) oxide and hydrogen gas.[2]
SECTION C – PHYSICS
Q28.
The power of a concave lens of focal length 50 cm is:[1]
Q29.
When a narrow beam of white light passes through a glass prism, it splits into seven component colours. This phenomenon occurs because:[1]
Q30.
If the electric current flowing through a fixed resistor is doubled, the rate of heat generation in the resistor will:[1]
Q31.
The magnetic field lines outside a permanent bar magnet:[1]
Q32.Assertion (A):
A rainbow is a natural optical spectrum appearing in the sky after a rain shower.
Reason (R): Tiny suspended water droplets act like miniature prisms that disperse, refract, and internally reflect sunlight.[1]
Reason (R): Tiny suspended water droplets act like miniature prisms that disperse, refract, and internally reflect sunlight.[1]
Q33.Assertion (A):
Commercial electric motors use an electromagnet in place of a permanent magnet.
Reason (R): Electromagnets provide a much stronger and adjustable magnetic field compared to permanent magnets.[1]
Reason (R): Electromagnets provide a much stronger and adjustable magnetic field compared to permanent magnets.[1]
Q34.
An electric heater of resistance $8\ \Omega$ draws a current of $15\text{ A}$ from the service mains. Calculate the rate at which heat is developed in the heater.[2]
Q35.
Define 1 Dioptre of power of a lens. What is the focal length of a lens having a power of $-2.5\text{ D}$?[2]
OR
State the two fundamental laws of reflection of light.Q36.(a) Why do stars twinkle at night, while planets do not?
(b) Why does the sky appear pitch dark instead of blue to an astronaut orbiting in outer space?[3]
(b) Why does the sky appear pitch dark instead of blue to an astronaut orbiting in outer space?[3]
Q37.(a) State the role of split rings (commutator) and carbon brushes in an electric motor.
(b) What is an electromagnet? Why is soft iron chosen as the core material of an electromagnet?[3]
(b) What is an electromagnet? Why is soft iron chosen as the core material of an electromagnet?[3]
Q38. Read the following passage and answer the questions:[4]
(b) What is the potential difference between the live wire and the neutral wire in standard Indian domestic power supply?
(c) Explain the safety function of an Earth wire connected to metallic appliances like electric irons or refrigerators.
OR
An electric appliance rated $2\text{ kW}, 220\text{ V}$ is operated in a domestic circuit with a $5\text{ A}$ fuse. What will happen when the appliance is turned on? Justify with calculation.
In domestic electric circuits, electricity is supplied through mains consisting of three wires: Live wire (red insulation, at 220 V), Neutral wire (black insulation, at zero potential), and Earth wire (green insulation). When live and neutral wires come in direct contact due to faulty insulation, the resistance of the circuit drops almost to zero, causing an enormous surge of current called short-circuiting. Overloading occurs when too many high-power appliances are connected simultaneously to a single socket.
(a) What is short-circuiting in an electric circuit?(b) What is the potential difference between the live wire and the neutral wire in standard Indian domestic power supply?
(c) Explain the safety function of an Earth wire connected to metallic appliances like electric irons or refrigerators.
OR
An electric appliance rated $2\text{ kW}, 220\text{ V}$ is operated in a domestic circuit with a $5\text{ A}$ fuse. What will happen when the appliance is turned on? Justify with calculation.
Q39.(a) An object $4.0\text{ cm}$ in size is placed at $25.0\text{ cm}$ in front of a concave mirror of focal length $15.0\text{ cm}$. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Find the nature and size of the image.
(b) Draw a neat ray diagram to show the formation of the image in this case.
(c) Write two everyday uses of concave mirrors.[5]
(b) In the circuit given below, three resistors of $10\ \Omega, 20\ \Omega,$ and $30\ \Omega$ are connected in parallel to a $12\text{ V}$ battery. Calculate:
(i) The total equivalent resistance of the circuit.
(ii) The total current drawn from the battery.
(iii) The current flowing through the $10\ \Omega$ resistor.
(b) Draw a neat ray diagram to show the formation of the image in this case.
(c) Write two everyday uses of concave mirrors.[5]
OR
(a) Derive the expression for the equivalent resistance $R_p$ of three resistors $R_1, R_2,$ and $R_3$ connected in parallel across a potential difference $V$.(b) In the circuit given below, three resistors of $10\ \Omega, 20\ \Omega,$ and $30\ \Omega$ are connected in parallel to a $12\text{ V}$ battery. Calculate:
(i) The total equivalent resistance of the circuit.
(ii) The total current drawn from the battery.
(iii) The current flowing through the $10\ \Omega$ resistor.
CBSE CLASS X SCIENCE – COMPLETE SOLUTIONS & MARKING SCHEME (SET – 9)
SECTION A – BIOLOGY SOLUTIONS
Q1. (b) Ethanol, carbon dioxide, and energy [1 Mark]
Explanation: Yeast cells carry out anaerobic alcoholic fermentation in the absence of oxygen, converting pyruvate into ethanol, $CO_2$, and 2 ATP molecules.
Explanation: Yeast cells carry out anaerobic alcoholic fermentation in the absence of oxygen, converting pyruvate into ethanol, $CO_2$, and 2 ATP molecules.
Q2. (a) Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector [1 Mark]
Explanation: The reflex arc starts at the sensory receptor, travels along the afferent sensory neuron into the spinal cord, passes across relay neurons, exits via the motor neuron, and stimulates the effector muscle.
Explanation: The reflex arc starts at the sensory receptor, travels along the afferent sensory neuron into the spinal cord, passes across relay neurons, exits via the motor neuron, and stimulates the effector muscle.
Q3. (c) Regeneration [1 Mark]
Explanation: Planaria has specialized stem-like cells that proliferate and differentiate to regenerate complete new individuals from cut fragments.
Explanation: Planaria has specialized stem-like cells that proliferate and differentiate to regenerate complete new individuals from cut fragments.
Q4. (b) One X chromosome [1 Mark]
Explanation: Human females are homogametic ($XX$), so every haploid ovum produced through meiosis carries exactly 22 autosomes and one $X$ sex chromosome.
Explanation: Human females are homogametic ($XX$), so every haploid ovum produced through meiosis carries exactly 22 autosomes and one $X$ sex chromosome.
Q5. (a) O₂ $\xrightarrow{\text{UV}}$ O + O ; followed by O + O₂ $\rightarrow$ O₃ [1 Mark]
Explanation: High-energy UV radiation splits molecular oxygen into nascent oxygen atoms ($O$). A free oxygen atom then combines with intact molecular oxygen ($O_2$) to form ozone ($O_3$).
Explanation: High-energy UV radiation splits molecular oxygen into nascent oxygen atoms ($O$). A free oxygen atom then combines with intact molecular oxygen ($O_2$) to form ozone ($O_3$).
Q6. (b) Transpiration pull [1 Mark]
Explanation: Evaporation of water molecules from leaf stomatal cells creates a continuous negative suction pressure (transpiration pull) that pulls water up from the roots through xylem conduits.
Explanation: Evaporation of water molecules from leaf stomatal cells creates a continuous negative suction pressure (transpiration pull) that pulls water up from the roots through xylem conduits.
Q7. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: The pancreas possesses exocrine acinar cells that secrete pancreatic juice via the pancreatic duct and endocrine islets of Langerhans that secrete insulin and glucagon directly into blood capillaries.
Explanation: The pancreas possesses exocrine acinar cells that secrete pancreatic juice via the pancreatic duct and endocrine islets of Langerhans that secrete insulin and glucagon directly into blood capillaries.
Q8. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Decomposers (bacteria and fungi) break down complex organic molecules from dead flora and fauna into simple inorganic substances, returning them to soil and air for reuse by producers.
Explanation: Decomposers (bacteria and fungi) break down complex organic molecules from dead flora and fauna into simple inorganic substances, returning them to soil and air for reuse by producers.
Q9. Autotrophic vs Heterotrophic Nutrition: [2 Marks]
- Autotrophic Nutrition: Organisms synthesise their own organic food from simple inorganic raw materials ($CO_2$ and $H_2O$) using sunlight energy. Example: Green plants, cyanobacteria. [1 Mark]
- Heterotrophic Nutrition: Organisms cannot synthesise their own food and depend directly or indirectly on autotrophs for organic carbon and chemical energy. Example: Animals, fungi, humans. [1 Mark]
Q10. Advantage of Sexual Reproduction: [2 Marks]
- Sexual reproduction involves the fusion of gametes from two genetically distinct individuals along with meiotic crossing-over, generating rich genetic variations in the offspring. [1 Mark]
- These variations provide adaptability and diversity, enabling some individuals of a species to survive environmental changes, disease outbreaks, and evolutionary pressures. [1 Mark]
Q11. Tropism and Plant Movements: [3 Marks]
- (a) Tropism: The directional growth movement of a plant organ in response to an external directional stimulus (e.g., light, gravity, water). [1 Mark]
- (b) Demonstration: Place a potted plant horizontally in a dark box with light entering from a side window. After a few days, the shoot bends upwards and towards the light source, demonstrating positive phototropism and negative geotropism. [1 Mark]
- (c) Gibberellins promote stem elongation, leaf expansion, and breaking seed dormancy. [1 Mark]
Q12. Monohybrid Cross on Pod Colour: [3 Marks]
- (a) F₁ Generation: Genotype = $Gg$; Phenotype = Green pods (100%). [1 Mark]
- (b) Punnett Square (F₁ selfing: $Gg \times Gg$):
[1 Mark]G g G GG Gg g Gg gg - (c) Ratios:
- Genotypic Ratio = 1 $GG$ : 2 $Gg$ : 1 $gg$ (1 : 2 : 1). [0.5 Mark]
- Phenotypic Ratio = 3 Green : 1 Yellow (3 : 1). [0.5 Mark]
Q13. Lymph (Tissue Fluid): [3 Marks]
- Formation: As blood flows through capillaries, some fluid, small proteins, and white blood cells leak through capillary pores into intercellular spaces to form interstitial fluid or lymph. [1 Mark]
- Functions:
- Absorbs and transports digested fats from the lacteals of the small intestine villi into the venous circulation. [1 Mark]
- Contains lymphocytes that fight infections and drains excess extracellular fluid back into systemic blood. [1 Mark]
Q14. Case-Based Solutions (Biology): [4 Marks]
- (a) Hormone: Insulin; Endocrine gland: Pancreas (Islets of Langerhans). [1 Mark]
- (b) Insulin is a protein hormone; if taken orally, it would be digested and inactivated by proteolytic enzymes (pepsin and trypsin) in the stomach and small intestine before reaching the bloodstream. [1 Mark]
- (c) Feedback Mechanism: When blood glucose levels rise, the beta cells of the pancreas detect this increase and respond by secreting insulin, which facilitates glucose uptake by cells. As blood glucose levels fall to normal, insulin secretion is reduced. [2 Marks]
- Master Gland: Pituitary Gland (Hypophysis). [1 Mark]
- Growth Hormone (GH) regulates the growth and development of bones, muscles, and body tissues. Deficiency in childhood causes dwarfism, whereas hypersecretion leads to gigantism. [1 Mark]
Q15. Long Answer (Biology): [5 Marks]
- (a) Alimentary Canal Diagram: Neat drawing correctly labelling Mouth/Oesophagus, Stomach, Liver, Gall bladder, Pancreas, Small intestine, Large intestine, and Rectum/Anus. [2 Marks]
- (b) Digestion Process:
- In Stomach: Gastric glands secrete $HCl$ (creates acidic pH ~1.5–2.0), pepsin (digests proteins into peptones), and mucus (protects gastric mucosa). [1 Mark]
- In Small Intestine: Bile emulsifies fats; pancreatic juice acts (trypsin digests proteins, lipase digests fats, amylase digests starch); intestinal wall enzymes complete the breakdown into amino acids, glucose, and fatty acids/glycerol. [1 Mark]
- (c) Intestinal juice contains peptidase, maltase, sucrase, and lipase that complete the conversion of all macromolecules into their simplest absorbable monomers. [1 Mark]
- (a) Sperm Structure: Diagram showing Head (with acrosome and nucleus), Middle piece (with spiral mitochondria for energy), and Tail (flagellum for motility). [2 Marks]
- (b) Contraceptive Methods:
- IUCDs (Copper-T): Placed inside the uterus by healthcare professionals; releases copper ions that suppress sperm motility and fertilising capacity, and prevents implantation. [1 Mark]
- Oral Pills: Contain synthetic hormones (progesterone/oestrogen) that alter hormonal balance to inhibit ovulation and alter cervical mucus to prevent sperm entry. [1 Mark]
- (c) Advantages: (i) Improves maternal and child health by proper spacing between births; (ii) Helps control population growth and ensures better economic resources for families. [1 Mark]
SECTION B – CHEMISTRY SOLUTIONS
Q16. (c) Greater than 7 (basic) [1 Mark]
Explanation: Sodium acetate is a salt of a weak acid ($CH_3COOH$) and a strong base ($NaOH$). On hydrolysis in water, it forms excess $OH^-$ ions, yielding a basic solution with $\text{pH} > 7$.
Explanation: Sodium acetate is a salt of a weak acid ($CH_3COOH$) and a strong base ($NaOH$). On hydrolysis in water, it forms excess $OH^-$ ions, yielding a basic solution with $\text{pH} > 7$.
Q17. (b) MnO₂ [1 Mark]
Explanation: $MnO_2$ supplies oxygen to oxidise $HCl$ to $Cl_2$, while $MnO_2$ itself is reduced to $MnCl_2$, making it the oxidising agent.
Explanation: $MnO_2$ supplies oxygen to oxidise $HCl$ to $Cl_2$, while $MnO_2$ itself is reduced to $MnCl_2$, making it the oxidising agent.
Q18. (c) Mercury [1 Mark]
Explanation: Cinnabar is mercuric sulphide ($HgS$), the primary natural ore from which mercury metal is extracted.
Explanation: Cinnabar is mercuric sulphide ($HgS$), the primary natural ore from which mercury metal is extracted.
Q19. (b) Propanoic acid [1 Mark]
Explanation: The compound contains 3 carbon atoms with a carboxylic acid functional group ($-COOH$), so its IUPAC name is propanoic acid.
Explanation: The compound contains 3 carbon atoms with a carboxylic acid functional group ($-COOH$), so its IUPAC name is propanoic acid.
Q20. (c) Single displacement reaction [1 Mark]
Explanation: Iron, being more reactive than copper, displaces copper from copper sulphate solution: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$.
Explanation: Iron, being more reactive than copper, displaces copper from copper sulphate solution: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$.
Q21. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Dissolving concentrated acid in water releases large amounts of heat. Adding water to acid can cause the mixture to splash out and break glass containers. Adding acid to water distributes the heat safely.
Explanation: Dissolving concentrated acid in water releases large amounts of heat. Adding water to acid can cause the mixture to splash out and break glass containers. Adding acid to water distributes the heat safely.
Q22. Rancidity and Prevention: [2 Marks]
- Rancidity: The slow oxidation of oils and fats present in food items exposed to air, resulting in unpleasant odor, bad taste, and spoilage. [1 Mark]
- Methods of Prevention: (i) Adding synthetic antioxidants like BHA/BHT; (ii) Flushing food packages with inert nitrogen gas; (iii) Storing food in airtight containers in refrigerators. [1 Mark]
Q23. Extraction of Zinc from Zinc Blende: [3 Marks]
- Roasting: The sulphide ore is heated strongly in the presence of excess air to convert it into zinc oxide:
$2ZnS(s) + 3O_2(g) \xrightarrow{\Delta} 2ZnO(s) + 2SO_2(g)\uparrow$ [1.5 Marks] - Reduction: Zinc oxide is then reduced to metallic zinc by heating with carbon (coke):
$ZnO(s) + C(s) \xrightarrow{\Delta} Zn(g) + CO(g)\uparrow$ [1.5 Marks]
- Properties of Ionic Compounds:
- High melting and boiling points: Strong electrostatic forces of attraction between oppositely charged ions require large amounts of heat energy to overcome. [1 Mark]
- Hard and brittle solids: Regular crystal lattice structure of alternating cations and anions resists deformation, but sudden shear forces shift like-charges next to each other, causing repulsion and cleavage. [1 Mark]
- Electrical conductivity in molten/aqueous state: In molten state or aqueous solution, free ions are mobile and conduct electricity, whereas in solid state, ions are fixed in lattice positions. [1 Mark]
Q24. Homologous Series and Hydrocarbons: [3 Marks]
- (a) Homologous Series: A family of organic compounds sharing the same functional group and similar chemical properties, where successive members differ by a $-CH_2-$ group (14 u). [1 Mark]
- (b) Cyclohexane ($C_6H_{12}$): A closed ring of 6 carbon atoms, each single-bonded to two neighboring carbons and two hydrogen atoms. [1 Mark]
- (c) Bromine Water Test: Unsaturated hydrocarbons (alkenes) decolourise red-brown bromine water through an addition reaction, whereas saturated hydrocarbons (alkanes) do not react or decolourise bromine water in the absence of UV light. [1 Mark]
Q25. Case-Based Solutions (Chemistry): [4 Marks]
- (a) Acid rain is precipitation with a pH lower than 5.6, caused by dissolved atmospheric pollutants like $SO_2$ and $NO_2$ forming sulphuric and nitric acids. [1 Mark]
- (b) Apply a mild basic paste like Baking soda ($NaHCO_3$) or calamine solution. It neutralises the acidic methanoic acid injected by the sting, providing relief from burning pain. [1.5 Marks]
- (c) Acid rain lowers the pH of river/lake water. Most aquatic organisms survive within a narrow pH range (~6.5–8.0); high acidity damages fish gills, kills fish eggs, and leaches toxic aluminium ions into water. [1.5 Marks]
- Nettle plant leaves have stinging hair that inject methanoic (formic) acid upon accidental contact, causing painful burning. Nature provides a natural remedy growing alongside nettles: the dock plant, whose leaves contain mild basic sap. Rubbing dock leaves over the stung area neutralises the acid. [2 Marks]
Q26. Long Answer (Chemistry): [5 Marks]
- (a) Bleaching Powder Preparation: Produced by passing dry chlorine gas over dry slaked lime:
$Ca(OH)_2(s) + Cl_2(g) \rightarrow CaOCl_2(s) + H_2O(l)$ [1.5 Marks] - (b) Solvay Process for Baking Soda:
$NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$ [1.5 Marks] - (c) Heating Baking Soda:
$2NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + H_2O(g) + CO_2(g)\uparrow$ [1 Mark] - (d) Uses of POP: (i) Used as plaster for supporting fractured bones; (ii) Used for making decorative moulds, statues, and smooth wall finishes. [1 Mark]
- (a) Soaps vs Detergents: Soaps are sodium/potassium salts of long-chain fatty acids that form scum in hard water. Detergents are sodium salts of long-chain alkyl benzene sulphonates or sulphates that lather freely in both soft and hard water. [1.5 Marks]
- (b) Cleansing Action: Soap molecules have hydrophilic ionic heads ($-COO^-Na^+$) and hydrophobic hydrocarbon tails. In water, tails attach to oily dirt while heads interact with water, forming spherical micelles. Agitation lifts dirt off fabric, and it is rinsed away. (Accompanying diagram). [2.5 Marks]
- (c) Hard water contains dissolved $Ca^{2+}$ and $Mg^{2+}$ ions that react with soap molecules to form insoluble grey-white precipitates called scum ($2C_{17}H_{35}COO^-Na^+ + Ca^{2+} \rightarrow (C_{17}H_{35}COO)_2Ca\downarrow + 2Na^+$). [1 Mark]
Q27. Balanced Chemical Equations: [2 Marks]
- (a) $CaCO_3(s) \xrightarrow{\Delta} CaO(s) + CO_2(g)\uparrow$ [1 Mark]
- (b) $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)\uparrow$ [1 Mark]
SECTION C – PHYSICS SOLUTIONS
Q28. (b) -2.0 D [1 Mark]
Explanation: For a concave lens, $f = -50\text{ cm} = -0.5\text{ m}$. Power $P = \frac{1}{f\text{ (in m)}} = \frac{1}{-0.5} = -2.0\text{ D}$.
Explanation: For a concave lens, $f = -50\text{ cm} = -0.5\text{ m}$. Power $P = \frac{1}{f\text{ (in m)}} = \frac{1}{-0.5} = -2.0\text{ D}$.
Q29. (a) Different colours of light have different speeds in glass and refract through different angles [1 Mark]
Explanation: The refractive index of glass varies slightly with wavelength; violet light travels slowest and bends most, whereas red light travels fastest and bends least.
Explanation: The refractive index of glass varies slightly with wavelength; violet light travels slowest and bends most, whereas red light travels fastest and bends least.
Q30. (c) Become four times [1 Mark]
Explanation: Rate of heat generation (power) is given by $H/t = P = I^2 R$. When current $I$ is doubled to $2I$, power becomes $(2I)^2 R = 4 I^2 R$, i.e., 4 times.
Explanation: Rate of heat generation (power) is given by $H/t = P = I^2 R$. When current $I$ is doubled to $2I$, power becomes $(2I)^2 R = 4 I^2 R$, i.e., 4 times.
Q31. (a) Emerge from North pole and merge at South pole [1 Mark]
Explanation: By convention, magnetic field lines outside a bar magnet emerge from the North pole and enter the South pole, forming closed continuous loops inside the magnet from South to North.
Explanation: By convention, magnetic field lines outside a bar magnet emerge from the North pole and enter the South pole, forming closed continuous loops inside the magnet from South to North.
Q32. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Raindrops act as small prisms: sunlight entering a drop undergoes refraction and dispersion, followed by internal reflection at the back of the droplet, and finally refraction again as it exits into the air.
Explanation: Raindrops act as small prisms: sunlight entering a drop undergoes refraction and dispersion, followed by internal reflection at the back of the droplet, and finally refraction again as it exits into the air.
Q33. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Electromagnets generate significantly stronger and controllable magnetic flux compared to permanent magnets, providing the high mechanical torque needed in industrial electric motors.
Explanation: Electromagnets generate significantly stronger and controllable magnetic flux compared to permanent magnets, providing the high mechanical torque needed in industrial electric motors.
Q34. Rate of Heat Development Calculation: [2 Marks]
Given: $R = 8\ \Omega$, $I = 15\text{ A}$.
Rate of heat developed is Power ($P = I^2 R$):
$P = (15\text{ A})^2 \times 8\ \Omega = 225 \times 8 = \mathbf{1800\text{ W}}$ (or $1800\text{ J/s}$). [2 Marks]
Given: $R = 8\ \Omega$, $I = 15\text{ A}$.
Rate of heat developed is Power ($P = I^2 R$):
$P = (15\text{ A})^2 \times 8\ \Omega = 225 \times 8 = \mathbf{1800\text{ W}}$ (or $1800\text{ J/s}$). [2 Marks]
Q35. 1 Dioptre Definition & Calculation: [2 Marks]
Laws of Reflection: (i) The incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence all lie in the same plane; (ii) The angle of incidence is always equal to the angle of reflection ($\angle i = \angle r$). [2 Marks]
- 1 Dioptre: The power of a lens having a focal length of exactly 1 metre ($1\text{ D} = 1\text{ m}^{-1}$). [1 Mark]
- Given: $P = -2.5\text{ D} \implies f = \frac{1}{P} = \frac{1}{-2.5} = -\frac{10}{25}\text{ m} = \mathbf{-0.4\text{ m}}$ (or $-40\text{ cm}$, concave lens). [1 Mark]
Laws of Reflection: (i) The incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence all lie in the same plane; (ii) The angle of incidence is always equal to the angle of reflection ($\angle i = \angle r$). [2 Marks]
Q36. Atmospheric Optics: [3 Marks]
- (a) Twinkling of Stars: Starlight passes through turbulent atmospheric layers with constantly fluctuating temperatures and refractive indices, causing continuous random shifts in the apparent position and brightness of the point-sized star. Planets are much closer and act as extended disc sources; variations from individual points average out, preventing twinkling. [2 Marks]
- (b) Sky to Astronaut: In outer space, there is no atmosphere and no gas or dust particles to cause Rayleigh scattering of sunlight. In the absence of scattered light, the sky appears completely dark/black. [1 Mark]
Q37. Electric Motor and Electromagnet: [3 Marks]
- (a) Split Rings (Commutator): Reverses the direction of current in the armature coil every half-rotation to maintain unidirectional torque. Carbon Brushes: Maintain continuous sliding electrical contact between rotating split rings and the stationary DC power source. [1.5 Marks]
- (b) Electromagnet: A temporary magnet consisting of a current-carrying solenoid with a soft iron core. Soft iron has high magnetic permeability (easily magnetised) and low retentivity (instantly demagnetises when current is switched off), making it an ideal core. [1.5 Marks]
Q38. Case-Based Solutions (Physics): [4 Marks]
- (a) Short-circuiting occurs when live and neutral wires come in direct contact due to damaged insulation, causing circuit resistance to drop to near zero and producing an abrupt, dangerous surge in electric current. [1 Mark]
- (b) The potential difference is 220 V (Live wire is at 220 V and Neutral wire is at 0 V). [1 Mark]
- (c) The Earth wire connects the metallic outer casing of an appliance to a metal plate buried deep in the ground, providing a low-resistance path for any leakage current, safely tripping the circuit and preventing electric shocks. [2 Marks]
- Power $P = 2\text{ kW} = 2000\text{ W}$, Voltage $V = 220\text{ V}$.
Current drawn: $I = \frac{P}{V} = \frac{2000}{220} \approx \mathbf{9.09\text{ A}}$. [1 Mark]
Because the current drawn ($9.09\text{ A}$) is much higher than the fuse capacity ($5\text{ A}$), the excessive current will immediately melt the fuse wire and safely break the circuit. [1 Mark]
Q39. Long Answer (Physics): [5 Marks]
- (a) Mirror Formula Calculation:
Given: $h_o = +4.0\text{ cm}$, $u = -25.0\text{ cm}$, $f = -15.0\text{ cm}$.
$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} – \frac{1}{u} = \frac{1}{-15.0} – \frac{1}{-25.0} = -\frac{1}{15} + \frac{1}{25} = \frac{-5 + 3}{75} = -\frac{2}{75}$
$\implies v = -\frac{75}{2}\text{ cm} = \mathbf{-37.5\text{ cm}}$.
The screen should be placed at $37.5\text{ cm}$ in front of the mirror. [1.5 Marks]
Magnification: $m = -\frac{v}{u} = -\frac{-37.5}{-25.0} = -1.5$
Height of image: $h_i = m \times h_o = -1.5 \times 4.0\text{ cm} = \mathbf{-6.0\text{ cm}}$.
Nature: Real, inverted, and magnified. [1 Mark] - (b) Ray Diagram: Neat drawing showing an object between $C$ and $F$ forming a real, inverted, magnified image beyond $C$. [1.5 Marks]
- (c) Uses: (i) In torches and vehicle headlights to get powerful parallel beams of light; (ii) As dentist mirrors to see enlarged images of teeth. [1 Mark]
- (a) Parallel Combination Derivation:
In parallel connection, the potential difference $V$ across each resistor is identical.
Total current $I = I_1 + I_2 + I_3$.
By Ohm’s law: $I_1 = \frac{V}{R_1}, I_2 = \frac{V}{R_2}, I_3 = \frac{V}{R_3}$, and $I = \frac{V}{R_p}$.
Substituting: $\frac{V}{R_p} = \frac{V}{R_1} + \frac{V}{R_2} + \frac{V}{R_3} \implies \mathbf{\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}}$. [2 Marks] - (b) Calculations:
- (i) $\frac{1}{R_p} = \frac{1}{10} + \frac{1}{20} + \frac{1}{30} = \frac{6 + 3 + 2}{60} = \frac{11}{60} \implies R_p = \frac{60}{11}\ \Omega \approx \mathbf{5.45\ \Omega}$. [1 Mark]
- (ii) Total current $I = \frac{V}{R_p} = \frac{12\text{ V}}{60/11\ \Omega} = \frac{12 \times 11}{60} = \mathbf{2.2\text{ A}}$. [1 Mark]
- (iii) Current through $10\ \Omega$ resistor: $I_{10} = \frac{V}{R_1} = \frac{12\text{ V}}{10\ \Omega} = \mathbf{1.2\text{ A}}$. [1 Mark]