ADEPT YOURSELF
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CBSE CLASS X – SCIENCE SAMPLE QUESTION PAPER
SET – 8 | 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.
The breakdown of pyruvate to give carbon dioxide, water, and energy takes place in the:[1]
Q2.
Which part of the sensory neuron receives incoming information and electrical signals?[1]
Q3.
In which of the following organisms does fragmentation occur as an effective mode of asexual reproduction?[1]
Q4.
If a round green seeded pea plant (RRyy) is crossed with a wrinkled yellow seeded pea plant (rrYY), the seeds produced in the F₁ generation will be:[1]
Q5.
Which group of organisms forms the second trophic level in any aquatic food chain?[1]
Q6.
Which of the following is an example of positive geotropism in higher plants?[1]
Q7.Assertion (A):
The separation of the right side and the left side of the human heart is useful to prevent oxygenated and deoxygenated blood from mixing.
Reason (R): Such separation allows a highly efficient supply of oxygen to the body, which is essential for warm-blooded animals with high energy needs.[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): Such separation allows a highly efficient supply of oxygen to the body, which is essential for warm-blooded animals with high energy needs.[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):
Acquired traits experienced by an individual during their lifetime cannot be passed on to the next generation.
Reason (R): Changes in non-reproductive somatic tissues cannot alter the DNA sequence of germ cells.[1]
Reason (R): Changes in non-reproductive somatic tissues cannot alter the DNA sequence of germ cells.[1]
Q9.
Why do herbivores feeding on grass require a longer small intestine compared to carnivores that feed on meat?[2]
Q10.
What is the function of the placenta during human pregnancy?[2]
Q11.(a) Name the plant growth regulator hormone synthesised at shoot tips that helps cells grow longer.
(b) What are nastic movements? How do they differ fundamentally from tropic movements?
(c) Name the growth hormone responsible for rapid cell division in fruits and seeds.[3]
(b) What are nastic movements? How do they differ fundamentally from tropic movements?
(c) Name the growth hormone responsible for rapid cell division in fruits and seeds.[3]
Q12.
A cross was made between pure breeding red-flowered pea plants ($RR$) and pure breeding white-flowered pea plants ($rr$).
(a) What flower colour will be observed in the F₁ generation?
(b) If F₁ plants are self-pollinated, write the genotypic and phenotypic ratios expected in the F₂ generation.
(c) State Mendel’s Law of Dominance based on this observation.[3]
(a) What flower colour will be observed in the F₁ generation?
(b) If F₁ plants are self-pollinated, write the genotypic and phenotypic ratios expected in the F₂ generation.
(c) State Mendel’s Law of Dominance based on this observation.[3]
Q13.
Trace the step-by-step pathway of blood flow through the four chambers of the human heart and the pulmonary and systemic circulations.[3]
Q14. Read the following passage and answer the questions:[4]
(b) Why are food chains generally limited to only 3 to 4 trophic steps?
(c) What will happen to the ecosystem if all top carnivores are completely removed from a food web?
OR
Construct a terrestrial food chain consisting of four trophic levels operating in a forest ecosystem and identify the top predator.
Food webs maintain ecological stability in terrestrial and aquatic biomes. In any food chain, green plants (autotrophs) capture light energy to produce carbohydrates. Herbivores feed on plants, and carnivores feed on herbivores. According to Lindeman’s 10 percent law, only about 10% of the energy entering a trophic level is converted into biomass and made available to the next trophic level, while the remaining 90% is lost as metabolic heat during respiration, digestion, and life processes. Because of this steep energy gradient, food chains rarely exceed four or five trophic levels.
(a) If 5,000 kJ of energy is available at the producer level in a grassland ecosystem, how much energy will be transferred to secondary consumers (carnivores)?(b) Why are food chains generally limited to only 3 to 4 trophic steps?
(c) What will happen to the ecosystem if all top carnivores are completely removed from a food web?
OR
Construct a terrestrial food chain consisting of four trophic levels operating in a forest ecosystem and identify the top predator.
Q15.(a) Draw a neat, well-labelled diagram of the human female reproductive system showing:
(i) Ovary (ii) Fallopian tube (Oviduct) (iii) Uterus (iv) Cervix
(b) What happens inside the female reproductive system when:
(i) The ovum is fertilised by a sperm?
(ii) The released ovum remains unfertilised?
(c) Name two surgical contraceptive methods practised in males and females respectively.[5]
(b) How is the amount of urine produced and excreted regulated by the human body?
(c) What is haemodialysis? State the underlying principle of an artificial kidney machine.
(i) Ovary (ii) Fallopian tube (Oviduct) (iii) Uterus (iv) Cervix
(b) What happens inside the female reproductive system when:
(i) The ovum is fertilised by a sperm?
(ii) The released ovum remains unfertilised?
(c) Name two surgical contraceptive methods practised in males and females respectively.[5]
OR
(a) Draw a neat labelled diagram of the human excretory system.(b) How is the amount of urine produced and excreted regulated by the human body?
(c) What is haemodialysis? State the underlying principle of an artificial kidney machine.
SECTION B – CHEMISTRY
Q16.
When dilute sulphuric acid is added to zinc granules in a conical flask, which gas is evolved with effervescence?[1]
Q17.
A drop of liquid sample turns blue litmus red and gives brisk effervescence with sodium hydrogen carbonate. The liquid is most likely:[1]
Q18.
Which of the following metals is extracted commercially by the electrolytic reduction of its molten oxide?[1]
Q19.
The general molecular formula for the alkyne homologous series containing a carbon-carbon triple bond is:[1]
Q20.
When copper metal powder is heated in a china dish, its surface turns black due to the formation of:[1]
Q21.Assertion (A):
Dry hydrogen chloride ($HCl$) gas does not change the colour of dry blue litmus paper.
Reason (R): Acids exhibit acidic properties and generate hydronium ions ($H_3O^+$) only in the presence of water.[1]
Reason (R): Acids exhibit acidic properties and generate hydronium ions ($H_3O^+$) only in the presence of water.[1]
Q22.
Translate the following word equation into a balanced chemical equation and write state symbols:
Barium chloride solution reacts with aluminium sulphate solution to form aluminium chloride solution and a white precipitate of barium sulphate.[2]
Barium chloride solution reacts with aluminium sulphate solution to form aluminium chloride solution and a white precipitate of barium sulphate.[2]
Q23.
Give reasons for each of the following:
(a) Platinum, gold, and silver are widely used to make jewellery.
(b) Highly reactive metals like sodium and potassium are stored immersed in kerosene oil.
(c) Aluminium metal is extensively used for making cooking utensils despite being high in the reactivity series.[3]
(b) Explain with a balanced chemical equation how zinc is extracted from its carbonate ore (calamine).
(a) Platinum, gold, and silver are widely used to make jewellery.
(b) Highly reactive metals like sodium and potassium are stored immersed in kerosene oil.
(c) Aluminium metal is extensively used for making cooking utensils despite being high in the reactivity series.[3]
OR
(a) Differentiate between a mineral and an ore.(b) Explain with a balanced chemical equation how zinc is extracted from its carbonate ore (calamine).
Q24.(a) Draw the structural formulas of propanone and propanal.
(b) State the functional group present in each of these compounds.
(c) Why do covalent carbon compounds have relatively low melting and boiling points?[3]
(b) State the functional group present in each of these compounds.
(c) Why do covalent carbon compounds have relatively low melting and boiling points?[3]
Q25. Read the following passage and answer the questions:[4]
(b) Write the chemical equation for the preparation of bleaching powder using one of the products of the chlor-alkali process.
(c) State two practical uses of sodium carbonate decahydrate ($Na_2CO_3 \cdot 10H_2O$).
OR
Explain how baking powder makes cakes and breads soft, fluffy, and spongy upon heating.
Common salt (Sodium Chloride, NaCl) obtained from sea water is an important raw material for producing various essential industrial chemicals. When electricity is passed through cold concentrated aqueous sodium chloride (brine), it decomposes to produce sodium hydroxide at the cathode, chlorine gas at the anode, and hydrogen gas at the cathode. Chlorine gas is subsequently used to produce bleaching powder with dry slaked lime, while sodium hydrogen carbonate and sodium carbonate are manufactured via the Solvay process using brine, ammonia, and carbon dioxide.
(a) Name the industrial process used to manufacture sodium hydroxide from brine.(b) Write the chemical equation for the preparation of bleaching powder using one of the products of the chlor-alkali process.
(c) State two practical uses of sodium carbonate decahydrate ($Na_2CO_3 \cdot 10H_2O$).
OR
Explain how baking powder makes cakes and breads soft, fluffy, and spongy upon heating.
Q26.(a) What are soaps chemically? Name the chemical reaction by which soaps are prepared.
(b) Write the balanced chemical equation representing the saponification of ethyl ethanoate with sodium hydroxide.
(c) Explain the combustion of saturated versus unsaturated hydrocarbons with respect to flame appearance and soot formation.[5]
(b) What is meant by water of crystallisation? How many water molecules are present in one formula unit of:
(i) Gypsum (ii) Blue vitriol (copper sulphate)
(c) A white powder ‘X’ is used by doctors to support fractured bones in the right position. Identify ‘X’, write its chemical formula, and state what happens when it is mixed with water.
(b) Write the balanced chemical equation representing the saponification of ethyl ethanoate with sodium hydroxide.
(c) Explain the combustion of saturated versus unsaturated hydrocarbons with respect to flame appearance and soot formation.[5]
OR
(a) Define a neutralisation reaction. Give two examples with balanced chemical equations.(b) What is meant by water of crystallisation? How many water molecules are present in one formula unit of:
(i) Gypsum (ii) Blue vitriol (copper sulphate)
(c) A white powder ‘X’ is used by doctors to support fractured bones in the right position. Identify ‘X’, write its chemical formula, and state what happens when it is mixed with water.
Q27.
A student adds dilute hydrochloric acid to granulated zinc. State two characteristic physical observations that confirm a chemical reaction has occurred.[2]
SECTION C – PHYSICS
Q28.
The absolute refractive index of a transparent medium is always:[1]
Q29.
The change in the focal length of an eye lens to focus objects at different distances is brought about by the action of the:[1]
Q30.
When three equal resistors each of resistance $R$ are connected in parallel, their equivalent resistance becomes:[1]
Q31.
The direction of the induced electric current in a conductor moving in a magnetic field is given by:[1]
Q32.Assertion (A):
A convex lens of focal length $f = +20\text{ cm}$ has a positive optical power of $+5\text{ D}$.
Reason (R): Power of a lens is defined as the reciprocal of its focal length in metres ($P = 1/f$).[1]
Reason (R): Power of a lens is defined as the reciprocal of its focal length in metres ($P = 1/f$).[1]
Q33.Assertion (A):
The magnetic field lines inside a current-carrying straight solenoid are parallel straight lines.
Reason (R): The magnetic field is uniform and identical in magnitude and direction at all points inside the solenoid.[1]
Reason (R): The magnetic field is uniform and identical in magnitude and direction at all points inside the solenoid.[1]
Q34.
A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position, and size of the image formed.[2]
Q35.
A piece of wire having resistance $R$ is cut into five equal parts. These five parts are then connected in parallel. If the equivalent resistance of this combination is $R’$, find the ratio $R / R’$.[2]
OR
Define electrical resistivity ($\rho$) of a conductor. State its standard SI unit.Q36.(a) What is presbyopia? Mention its causes.
(b) How is presbyopia corrected in older individuals who also suffer from myopia?
(c) Why do planets not twinkle like stars?[3]
(b) How is presbyopia corrected in older individuals who also suffer from myopia?
(c) Why do planets not twinkle like stars?[3]
Q37.
State the function of each of the following safety components in domestic electrical wiring circuits:
(a) Earth wire (b) Electric fuse (c) Miniature Circuit Breaker (MCB)[3]
(a) Earth wire (b) Electric fuse (c) Miniature Circuit Breaker (MCB)[3]
Q38. Read the following passage and answer the questions:[4]
(b) An electric heater of resistance $20\ \Omega$ takes a current of $5\text{ A}$ from the mains supply. Calculate the heat produced in $30\text{ seconds}$.
(c) An electric kettle consumes $1\text{ kW}$ of electric power when operated at $220\text{ V}$. Calculate the current rating of the fuse wire required for safe operation.
OR
Compare the resistance of a 100 W bulb with a 60 W bulb, both designed to operate at 220 V. Which bulb has thicker filament wire?
When an electric current flows through a metallic conductor, heat is generated due to collisions between flowing electrons and vibrating lattice atoms. The heat produced ($H$) in a conductor of resistance $R$ carrying current $I$ for time $t$ is given by Joule’s Law: $H = I^2 R t$. This thermal effect is utilised in domestic appliances such as electric irons, toasters, and immersion heaters fitted with nichrome heating coils. Alloys like nichrome are chosen because of their high electrical resistivity and high melting points that resist oxidation at elevated temperatures.
(a) Why is nichrome alloy preferred over copper for making heating elements of electric toasters and irons?(b) An electric heater of resistance $20\ \Omega$ takes a current of $5\text{ A}$ from the mains supply. Calculate the heat produced in $30\text{ seconds}$.
(c) An electric kettle consumes $1\text{ kW}$ of electric power when operated at $220\text{ V}$. Calculate the current rating of the fuse wire required for safe operation.
OR
Compare the resistance of a 100 W bulb with a 60 W bulb, both designed to operate at 220 V. Which bulb has thicker filament wire?
Q39.(a) State the laws of refraction of light.
(b) What is meant by the statement: “The refractive index of glass with respect to water is 1.125”?
(c) Light enters from air into a glass plate having a refractive index of 1.50. What is the speed of light in glass? (Speed of light in vacuum = $3 \times 10^8\text{ m/s}$).[5]
(b) State the Right-Hand Thumb rule (or Clock Face Rule) to determine the magnetic polarity of the faces of the circular loop.
(c) A current-carrying straight wire is placed in a uniform magnetic field. Under what geometric condition is the force experienced by the wire:
(i) Maximum?
(ii) Minimum (zero)?
(b) What is meant by the statement: “The refractive index of glass with respect to water is 1.125”?
(c) Light enters from air into a glass plate having a refractive index of 1.50. What is the speed of light in glass? (Speed of light in vacuum = $3 \times 10^8\text{ m/s}$).[5]
OR
(a) Draw the magnetic field pattern produced around a circular loop of wire carrying an electric current.(b) State the Right-Hand Thumb rule (or Clock Face Rule) to determine the magnetic polarity of the faces of the circular loop.
(c) A current-carrying straight wire is placed in a uniform magnetic field. Under what geometric condition is the force experienced by the wire:
(i) Maximum?
(ii) Minimum (zero)?
CBSE CLASS X SCIENCE – COMPLETE SOLUTIONS & MARKING SCHEME (SET – 8)
SECTION A – BIOLOGY SOLUTIONS
Q1. (b) Mitochondria [1 Mark]
Explanation: Aerobic breakdown of pyruvate into carbon dioxide, water, and energy (ATP) occurs inside the mitochondria of cells.
Explanation: Aerobic breakdown of pyruvate into carbon dioxide, water, and energy (ATP) occurs inside the mitochondria of cells.
Q2. (b) Dendrite [1 Mark]
Explanation: Dendrites are branched protoplasmic extensions of the neuron that receive incoming chemical stimuli and convert them into electrical impulses.
Explanation: Dendrites are branched protoplasmic extensions of the neuron that receive incoming chemical stimuli and convert them into electrical impulses.
Q3. (a) Spirogyra [1 Mark]
Explanation: Spirogyra is a multicellular filamentous green alga that simply breaks into smaller fragments upon maturation, each growing into a new filament.
Explanation: Spirogyra is a multicellular filamentous green alga that simply breaks into smaller fragments upon maturation, each growing into a new filament.
Q4. (a) Round and yellow [1 Mark]
Explanation: The F₁ progeny inherits genotype $RrYy$. Since Round ($R$) and Yellow ($Y$) are dominant over wrinkled ($r$) and green ($y$), all F₁ plants bear round yellow seeds.
Explanation: The F₁ progeny inherits genotype $RrYy$. Since Round ($R$) and Yellow ($Y$) are dominant over wrinkled ($r$) and green ($y$), all F₁ plants bear round yellow seeds.
Q5. (b) Zooplankton [1 Mark]
Explanation: In an aquatic ecosystem, microscopic photosynthetic algae (phytoplankton) form the 1st trophic level (producers), while primary consumers (zooplankton) occupy the 2nd trophic level.
Explanation: In an aquatic ecosystem, microscopic photosynthetic algae (phytoplankton) form the 1st trophic level (producers), while primary consumers (zooplankton) occupy the 2nd trophic level.
Q6. (a) Downward growth of roots into the soil [1 Mark]
Explanation: Plant roots grow downwards in the direction of gravitational pull, exhibiting positive geotropism.
Explanation: Plant roots grow downwards in the direction of gravitational pull, exhibiting positive geotropism.
Q7. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: The complete interventricular and interatrial septal partition prevents mixing of oxygen-rich and carbon-dioxide-rich blood, supporting high metabolic rates and endothermy in mammals and birds.
Explanation: The complete interventricular and interatrial septal partition prevents mixing of oxygen-rich and carbon-dioxide-rich blood, supporting high metabolic rates and endothermy in mammals and birds.
Q8. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Acquired characters only affect somatic body cells and do not alter the nucleotide sequence in the DNA of germ cells (gametes), making them non-inheritable.
Explanation: Acquired characters only affect somatic body cells and do not alter the nucleotide sequence in the DNA of germ cells (gametes), making them non-inheritable.
Q9. Small Intestine Length in Herbivores vs Carnivores: [2 Marks]
- Herbivores eat plant matter rich in cellulose, which is fibrous and difficult to digest; therefore, they have a longer small intestine to allow complete bacterial enzymatic digestion of cellulose. [1 Mark]
- Carnivores eat meat, which is rich in proteins and fats that are digested much more easily and quickly; hence, they have a shorter small intestine. [1 Mark]
Q10. Functions of Placenta: [2 Marks]
- Nutrition and Respiration: Provides a large surface area for the diffusion of glucose, amino acids, and oxygen from maternal blood to the developing embryo/foetus. [1 Mark]
- Excretion: Transports metabolic waste products (like urea, uric acid, and $CO_2$) generated by the foetus into the mother’s bloodstream for excretion. [1 Mark]
Q11. Hormones and Plant Movements: [3 Marks]
- (a) Auxin. [0.5 Mark]
- (b) Nastic vs Tropic Movements: Nastic movements are non-directional responses to stimuli where the direction of movement is independent of the stimulus direction (e.g., folding of touch-me-not leaves). Tropic movements are directional growth responses where the direction of movement depends strictly on the direction of stimulus (e.g., phototropism). [1.5 Marks]
- (c) Cytokinins. [1 Mark]
Q12. Monohybrid Cross (Flower Colour): [3 Marks]
- (a) F₁ Generation: All plants will produce Red flowers (Genotype: $Rr$). [1 Mark]
- (b) F₂ Generation:
- Phenotypic Ratio = 3 Red : 1 White. [0.5 Mark]
- Genotypic Ratio = 1 $RR$ : 2 $Rr$ : 1 $rr$ (1 : 2 : 1). [0.5 Mark]
- (c) Law of Dominance: When two alleles of an inherited pair are heterozygous, the allele that is expressed phenotypically is dominant ($R$), and the masked allele is recessive ($r$). [1 Mark]
Q13. Pathway of Blood Flow in Human Heart: [3 Marks]
- Deoxygenated blood from body tissues enters the Right Atrium via the vena cava. [0.5 Mark]
- Right atrium contracts, sending blood into the Right Ventricle, which pumps it to the lungs via the Pulmonary Artery for oxygenation (Pulmonary loop). [1 Mark]
- Oxygenated blood from the lungs returns through the Pulmonary Veins into the Left Atrium. [0.5 Mark]
- Left atrium contracts, pushing blood into the Left Ventricle, which pumps it under high pressure through the Aorta to all body tissues (Systemic loop). [1 Mark]
Q14. Case-Based Solutions (Biology): [4 Marks]
- (a) Energy at Producer level = $5000\text{ kJ}$
Primary Consumers (Herbivores) = $10\% \text{ of } 5000 = 500\text{ kJ}$
Secondary Consumers (Carnivores) = $10\% \text{ of } 500 = \mathbf{50\text{ kJ}}$. [1.5 Marks] - (b) Because 90% of energy is dissipated as metabolic heat at each trophic step, the amount of energy remaining after 4 trophic levels becomes too minuscule to sustain another higher trophic population. [1.5 Marks]
- (c) The population of herbivores would surge unchecked, leading to overgrazing, depletion of vegetation, habitat degradation, and ecological collapse. [1 Mark]
- Forest Food Chain: Green Plants/Trees (Trophic level 1) $\rightarrow$ Deer (Trophic level 2) $\rightarrow$ Jackal/Fox (Trophic level 3) $\rightarrow$ Tiger/Lion (Trophic level 4). [1 Mark]
- Top Predator: Tiger / Lion (Apex predator). [1 Mark]
Q15. Long Answer (Biology): [5 Marks]
- (a) Diagram: Neat diagram correctly labelling the Ovary, Fallopian tube (Oviduct), Uterus, and Cervix/Vagina. [2 Marks]
- (b) Events:
- (i) If fertilised: A diploid zygote forms, divides mitotically into an embryo, implants in the vascularised uterine lining, and develops into a foetus over gestation (~9 months). [1 Mark]
- (ii) If not fertilised: The thick uterine lining along with its blood vessels sheds and breaks down, discharging blood and mucus through the vagina as menstruation (lasting 3–5 days). [1 Mark]
- (c) Surgical Contraceptive Methods: Vasectomy in males (blocking vas deferens) and Tubectomy in females (blocking fallopian tubes). [1 Mark]
- (a) Diagram: Diagram of excretory system showing Left and Right Kidneys, Ureters, Urinary Bladder, Urethra, and Renal blood vessels. [2 Marks]
- (b) Urine Regulation: The quantity of urine produced depends on (i) the amount of excess water present in body tissues, (ii) the concentration of dissolved nitrogenous wastes to be excreted, and (iii) the action of antidiuretic hormone (ADH) that modulates tubular reabsorption. [1.5 Marks]
- (c) Haemodialysis: An artificial clinical procedure used to filter metabolic waste products (urea) and excess fluid from the blood of patients suffering from kidney failure. Blood passes through semipermeable cellophane tubes immersed in dialysing fluid having the same osmotic pressure as normal blood but devoid of nitrogenous waste. [1.5 Marks]
SECTION B – CHEMISTRY SOLUTIONS
Q16. (b) Hydrogen gas [1 Mark]
Explanation: $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g)\uparrow$. Zinc displaces hydrogen from dilute sulphuric acid.
Explanation: $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g)\uparrow$. Zinc displaces hydrogen from dilute sulphuric acid.
Q17. (c) Ethanoic acid [1 Mark]
Explanation: Ethanoic acid is acidic, turning blue litmus red, and releases $CO_2$ gas with brisk effervescence when reacting with $NaHCO_3$.
Explanation: Ethanoic acid is acidic, turning blue litmus red, and releases $CO_2$ gas with brisk effervescence when reacting with $NaHCO_3$.
Q18. (c) Aluminium [1 Mark]
Explanation: Aluminium has a high affinity for oxygen and cannot be reduced by carbon; it is extracted industrially by electrolytic reduction of molten alumina ($Al_2O_3$) via the Hall-Héroult process.
Explanation: Aluminium has a high affinity for oxygen and cannot be reduced by carbon; it is extracted industrially by electrolytic reduction of molten alumina ($Al_2O_3$) via the Hall-Héroult process.
Q19. (c) CₙH₂ₙ₋₂ [1 Mark]
Explanation: Alkynes contain one triple bond ($C\equiv C$) and have the general formula $C_n H_{2n-2}$ (for $n \ge 2$).
Explanation: Alkynes contain one triple bond ($C\equiv C$) and have the general formula $C_n H_{2n-2}$ (for $n \ge 2$).
Q20. (b) Copper(II) oxide [1 Mark]
Explanation: Heating copper metal in air causes oxidation: $2Cu(s) + O_2(g) \rightarrow 2CuO(s)$ (black copper(II) oxide).
Explanation: Heating copper metal in air causes oxidation: $2Cu(s) + O_2(g) \rightarrow 2CuO(s)$ (black copper(II) oxide).
Q21. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Dry HCl gas does not contain free hydrogen/hydronium ions. Acidic behaviour and indicator colour changes occur only in aqueous solution where HCl dissociates into $H_3O^+$ and $Cl^-$ ions.
Explanation: Dry HCl gas does not contain free hydrogen/hydronium ions. Acidic behaviour and indicator colour changes occur only in aqueous solution where HCl dissociates into $H_3O^+$ and $Cl^-$ ions.
Q22. Balanced Equation: [2 Marks]
$3BaCl_2(aq) + Al_2(SO_4)_3(aq) \rightarrow 3BaSO_4(s)\downarrow + 2AlCl_3(aq)$ [2 Marks]
$3BaCl_2(aq) + Al_2(SO_4)_3(aq) \rightarrow 3BaSO_4(s)\downarrow + 2AlCl_3(aq)$ [2 Marks]
Q23. Chemical Reasons: [3 Marks]
- (a) Platinum, gold, and silver are noble metals located at the bottom of the reactivity series; they are non-corrosive, unreactive to air/moisture, and retain high metallic lustre. [1 Mark]
- (b) Sodium and potassium are highly reactive and react violently and exothermically with atmospheric oxygen and moisture, catching fire. They are kept immersed in kerosene to isolate them from air and water. [1 Mark]
- (c) Aluminium reacts with atmospheric oxygen to form a thin, impervious, and self-healing protective layer of aluminium oxide ($Al_2O_3$) on its surface that prevents further corrosion. [1 Mark]
- (a) Mineral: Naturally occurring inorganic solid substance found in the Earth’s crust containing elements or compounds. Ore: A mineral from which a particular metal can be extracted profitably and conveniently. [1.5 Marks]
- (b) Extraction of Zinc from Calamine ($ZnCO_3$):
- Calcination: $ZnCO_3(s) \xrightarrow{\Delta} ZnO(s) + CO_2(g)$
- Reduction with Carbon: $ZnO(s) + C(s) \xrightarrow{\Delta} Zn(s) + CO(g)$ [1.5 Marks]
Q24. Structures and Bonding: [3 Marks]
- (a) Structures:
- Propanone: $CH_3-CO-CH_3$ [0.5 Mark]
- Propanal: $CH_3-CH_2-CHO$ [0.5 Mark]
- (b) Functional Groups: Propanone contains a Ketone group ($>C=O$); Propanal contains an Aldehyde group ($-CHO$). [1 Mark]
- (c) Covalent compounds consist of discrete molecules held together by weak intermolecular forces (van der Waals forces) that require small amounts of thermal energy to break. [1 Mark]
Q25. Case-Based Solutions (Chemistry): [4 Marks]
- (a) Chlor-alkali process. [1 Mark]
- (b) $Ca(OH)_2(s) + Cl_2(g) \rightarrow CaOCl_2(s) + H_2O(l)$ [1 Mark]
- (c) Uses of Washing Soda: (i) Removing permanent hardness of water; (ii) Manufacturing glass, soap, and paper. [2 Marks]
- Baking powder is a mixture of baking soda ($NaHCO_3$) and a mild edible acid (tartaric acid). On heating with moisture during baking, the reaction generates carbon dioxide gas:
$NaHCO_3 + H^+ \rightarrow Na^+ + H_2O + CO_2\uparrow$
The released $CO_2$ gas bubbles expand and get trapped in the batter, causing bread and cakes to rise and become light and spongy. [2 Marks]
Q26. Long Answer (Chemistry): [5 Marks]
- (a) Soaps are sodium or potassium salts of long-chain fatty acids (e.g., sodium stearate). The chemical reaction is known as Saponification. [1.5 Marks]
- (b) Saponification Equation:
$CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH$ [1.5 Marks] - (c) Combustion: Saturated hydrocarbons burn with a clean, blue, non-sooty flame due to complete combustion in adequate air. Unsaturated hydrocarbons burn with a yellow, smoky, sooty flame due to unburnt carbon particles resulting from higher carbon-to-hydrogen ratios. [2 Marks]
- (a) Neutralisation: The chemical reaction between an acid and a base to form salt and water.
Examples: (i) $HCl + NaOH \rightarrow NaCl + H_2O$; (ii) $H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O$. [1.5 Marks] - (b) Water of crystallisation: Fixed number of water molecules chemically bonded in one formula unit of a salt crystal. (i) Gypsum = 2 ($CaSO_4 \cdot 2H_2O$); (ii) Blue vitriol = 5 ($CuSO_4 \cdot 5H_2O$). [1.5 Marks]
- (c) Compound ‘X’ is Plaster of Paris (Calcium sulphate hemihydrate, $CaSO_4 \cdot \frac{1}{2}H_2O$).
When mixed with water, it rehydrates to form a hard solid mass of gypsum:
$CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$. [2 Marks]
Q27. Observations for Zinc + HCl Reaction: [2 Marks]
- Evolution of colourless and odourless gas bubbles with brisk effervescence (hydrogen gas). [1 Mark]
- The test tube or flask becomes warm to the touch due to the release of heat (exothermic reaction). [1 Mark]
SECTION C – PHYSICS SOLUTIONS
Q28. (c) Greater than 1 [1 Mark]
Explanation: Absolute refractive index $n = \frac{c}{v}$. Because the speed of light in vacuum ($c$) is the maximum possible speed and light always travels slower in any material medium ($v < c$), $n$ is always greater than 1.
Explanation: Absolute refractive index $n = \frac{c}{v}$. Because the speed of light in vacuum ($c$) is the maximum possible speed and light always travels slower in any material medium ($v < c$), $n$ is always greater than 1.
Q29. (c) Ciliary muscles [1 Mark]
Explanation: The ciliary muscles relax or contract to modify the curvature and focal length of the flexible crystalline lens (accommodation).
Explanation: The ciliary muscles relax or contract to modify the curvature and focal length of the flexible crystalline lens (accommodation).
Q30. (b) R / 3 [1 Mark]
Explanation: In parallel combination: $\frac{1}{R_p} = \frac{1}{R} + \frac{1}{R} + \frac{1}{R} = \frac{3}{R} \implies R_p = \frac{R}{3}$.
Explanation: In parallel combination: $\frac{1}{R_p} = \frac{1}{R} + \frac{1}{R} + \frac{1}{R} = \frac{3}{R} \implies R_p = \frac{R}{3}$.
Q31. (b) Fleming’s Right-Hand Rule [1 Mark]
Explanation: Fleming’s Right-Hand Rule gives the direction of induced electric current in a conductor moving inside a magnetic field.
Explanation: Fleming’s Right-Hand Rule gives the direction of induced electric current in a conductor moving inside a magnetic field.
Q32. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: $P = \frac{1}{f\text{ (in m)}} = \frac{1}{+0.20\text{ m}} = +5\text{ D}$.
Explanation: $P = \frac{1}{f\text{ (in m)}} = \frac{1}{+0.20\text{ m}} = +5\text{ D}$.
Q33. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Parallel, straight, equidistant field lines inside a current-carrying solenoid indicate a uniform magnetic field in both magnitude and direction.
Explanation: Parallel, straight, equidistant field lines inside a current-carrying solenoid indicate a uniform magnetic field in both magnitude and direction.
Q34. Convex Lens Numerical: [2 Marks]
Given: $h_o = +2.0\text{ cm}$, $f = +10\text{ cm}$, $u = -15\text{ cm}$.
Using Lens Formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} + \frac{1}{u}$
$\frac{1}{v} = \frac{1}{10} + \frac{1}{-15} = \frac{3 – 2}{30} = \frac{1}{30} \implies v = \mathbf{+30\text{ cm}}$ [1 Mark]
Magnification: $m = \frac{v}{u} = \frac{+30}{-15} = -2$
Height of image: $h_i = m \times h_o = -2 \times 2.0\text{ cm} = \mathbf{-4.0\text{ cm}}$
Nature: Real, inverted, and magnified, formed at $30\text{ cm}$ on the opposite side of the lens. [1 Mark]
Given: $h_o = +2.0\text{ cm}$, $f = +10\text{ cm}$, $u = -15\text{ cm}$.
Using Lens Formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} + \frac{1}{u}$
$\frac{1}{v} = \frac{1}{10} + \frac{1}{-15} = \frac{3 – 2}{30} = \frac{1}{30} \implies v = \mathbf{+30\text{ cm}}$ [1 Mark]
Magnification: $m = \frac{v}{u} = \frac{+30}{-15} = -2$
Height of image: $h_i = m \times h_o = -2 \times 2.0\text{ cm} = \mathbf{-4.0\text{ cm}}$
Nature: Real, inverted, and magnified, formed at $30\text{ cm}$ on the opposite side of the lens. [1 Mark]
Q35. Ratio of Resistance: [2 Marks]
When a wire of resistance $R$ is cut into 5 equal pieces, the resistance of each piece becomes $r = \frac{R}{5}$.
Connecting these 5 pieces in parallel gives:
$\frac{1}{R’} = \frac{1}{r} + \frac{1}{r} + \frac{1}{r} + \frac{1}{r} + \frac{1}{r} = \frac{5}{r} = \frac{5}{R/5} = \frac{25}{R} \implies R’ = \frac{R}{25}$
$\implies \frac{R}{R’} = \mathbf{25}$ (or $25 : 1$). [2 Marks]
OR
Electrical Resistivity ($\rho$): The resistance offered by a cylindrical conductor of unit length ($1\text{ m}$) and unit cross-sectional area ($1\text{ m}^2$). SI unit is Ohm-metre ($\Omega\cdot\text{m}$). [2 Marks]
When a wire of resistance $R$ is cut into 5 equal pieces, the resistance of each piece becomes $r = \frac{R}{5}$.
Connecting these 5 pieces in parallel gives:
$\frac{1}{R’} = \frac{1}{r} + \frac{1}{r} + \frac{1}{r} + \frac{1}{r} + \frac{1}{r} = \frac{5}{r} = \frac{5}{R/5} = \frac{25}{R} \implies R’ = \frac{R}{25}$
$\implies \frac{R}{R’} = \mathbf{25}$ (or $25 : 1$). [2 Marks]
OR
Electrical Resistivity ($\rho$): The resistance offered by a cylindrical conductor of unit length ($1\text{ m}$) and unit cross-sectional area ($1\text{ m}^2$). SI unit is Ohm-metre ($\Omega\cdot\text{m}$). [2 Marks]
Q36. Presbyopia and Planetary Twinkling: [3 Marks]
- (a) Presbyopia: Old-age defect of vision where the near point recedes, making reading difficult. Caused by gradual weakening of ciliary muscles and diminishing flexibility of crystalline eye lens. [1 Mark]
- (b) Corrected by using bi-focal lenses (upper portion is concave for distant vision and lower portion is convex for reading). [1 Mark]
- (c) Planets are much closer to Earth and act as extended optical sources. The total variation in the amount of light entering the eye from all individual point locations averages out to zero, nullifying the twinkling effect. [1 Mark]
Q37. Safety Components in Electrical Circuits: [3 Marks]
- (a) Earth Wire: Provides a low-resistance path for leakage current to flow safely into the ground, preventing severe electric shocks if metal casings become live. [1 Mark]
- (b) Electric Fuse: Safety device containing a low-melting-point wire that melts and breaks the circuit during overloading or short circuits. [1 Mark]
- (c) MCB: An electromagnetic switch that automatically trips open to break the circuit when excessive current flows through it. [1 Mark]
Q38. Case-Based Solutions (Physics): [4 Marks]
- (a) Nichrome has much higher resistivity than copper and does not oxidise (burn) easily even at high temperatures (red-hot stage). [1 Mark]
- (b) $H = I^2 R t = (5\text{ A})^2 \times 20\ \Omega \times 30\text{ s} = 25 \times 20 \times 30 = \mathbf{15,000\text{ J}}$ (or $15\text{ kJ}$). [1.5 Marks]
- (c) $I = \frac{P}{V} = \frac{1000\text{ W}}{220\text{ V}} \approx 4.54\text{ A}$. A fuse rated at 5 A must be used. [1.5 Marks]
- $R = \frac{V^2}{P} \implies R_{100\text{W}} = \frac{220^2}{100} = 484\ \Omega$ and $R_{60\text{W}} = \frac{220^2}{60} = 806.7\ \Omega$.
Since $R \propto \frac{1}{A}$, the 100 W bulb has lower resistance and therefore has a thicker filament. [2 Marks]
Q39. Long Answer (Physics): [5 Marks]
- (a) Laws of Refraction:
- The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane. [1 Mark]
- Snell’s Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for light of a given colour and pair of media: $\frac{\sin i}{\sin r} = \text{constant} = n_{21}$. [1 Mark]
- (b) It means that the ratio of the speed of light in water ($v_w$) to the speed of light in glass ($v_g$) is equal to 1.125 ($\frac{v_w}{v_g} = 1.125$). [1 Mark]
- (c) $n = \frac{c}{v_g} \implies v_g = \frac{c}{n} = \frac{3 \times 10^8\text{ m/s}}{1.50} = \mathbf{2 \times 10^8\text{ m/s}}$. [2 Marks]
- (a) Circular Loop Field Pattern: Field lines are concentric circles near the wire segments, expanding into nearly straight parallel lines near the centre of the loop. [2 Marks]
- (b) Clock Face Rule: Looking at a face of the loop, if the electric current flows in a clockwise direction, that face behaves as a South pole; if it flows in an anti-clockwise direction, it behaves as a North pole. [1.5 Marks]
- (c) Force $F = B I L \sin \theta$:
- (i) Maximum: When the conductor is placed perpendicular ($\theta = 90^\circ$) to the magnetic field. [0.75 Mark]
- (ii) Minimum (Zero): When the conductor is placed parallel or anti-parallel ($\theta = 0^\circ \text{ or } 180^\circ$) to the magnetic field. [0.75 Mark]