ADEPT YOURSELF
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CBSE CLASS X – SCIENCE SAMPLE QUESTION PAPER
SET – 10 | 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.
In which cell organelle does the light-dependent stage of photosynthesis occur in green plants?[1]
Q2.
Which region of the human brain contains reflex centres for coughing, sneezing, swallowing, and salivation?[1]
Q3.
Binary fission occurs in a definite, longitudinal orientation in which of the following organisms?[1]
Q4.
In humans, if a sperm carrying an X-chromosome fertilises an ovum, the resulting zygote will develop into a:[1]
Q5.
Which of the following materials is completely non-biodegradable and causes microplastic pollution in soil and marine ecosystems?[1]
Q6.
Which of the following sets represents primary consumers in terrestrial and pond ecosystems respectively?[1]
Q7.Assertion (A):
Blood platelets play a vital role in preventing haemorrhagic blood loss during physical injury.
Reason (R): Platelets release clotting factors that initiate a cascade to form a fibrin mesh at the site of a cut.[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): Platelets release clotting factors that initiate a cascade to form a fibrin mesh at the site of a cut.[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):
The accumulation of pesticide residues is highest in humans who eat grain and animal products.
Reason (R): Pesticides are biodegradable and degrade quickly as they pass up each trophic level.[1]
Reason (R): Pesticides are biodegradable and degrade quickly as they pass up each trophic level.[1]
Q9.
Why does bread taste sweet after being chewed for a few minutes in the mouth?[2]
Q10.
Mention two major differences between binary fission in Amoeba and budding in Yeast.[2]
Q11.(a) What is thigmotropism? Give one example of a plant organ exhibiting thigmotropism.
(b) Explain how auxins cause a pea plant tendril to coil tightly around an external support.
(c) Name the phytohormone that promotes fruit ripening.[3]
(b) Explain how auxins cause a pea plant tendril to coil tightly around an external support.
(c) Name the phytohormone that promotes fruit ripening.[3]
Q12.
A cross is carried out between a pure violet-flowered pea plant ($VV$) and a pure white-flowered pea plant ($vv$).
(a) What will be the flower colour of the plants in the F₁ generation?
(b) If the F₁ plants are allowed to self-pollinate, calculate the percentage of white-flowered plants expected in the F₂ generation.
(c) Write the phenotypic and genotypic ratios of the F₂ generation.[3]
(a) What will be the flower colour of the plants in the F₁ generation?
(b) If the F₁ plants are allowed to self-pollinate, calculate the percentage of white-flowered plants expected in the F₂ generation.
(c) Write the phenotypic and genotypic ratios of the F₂ generation.[3]
Q13.
What are stomata? Describe their role in gaseous exchange and transpiration, and explain how the movement of guard cells regulates their opening and closing.[3]
Q14. Read the following passage and answer the questions:[4]
(b) State two secondary sexual characteristics induced by testosterone in adolescent boys.
(c) Explain why the adrenal gland is commonly referred to as the “emergency gland” of the body.
OR
What is the role of progesterone secreted by the ovaries in the female reproductive cycle?
The human endocrine system controls and coordinates physiological processes via hormones. The thyroid gland situated in the neck requires dietary iodine to produce thyroxin, which regulates carbohydrate, fat, and protein metabolism. The adrenal glands secrete adrenaline to prepare the body for physical emergencies. In adolescent males and females, the testes secrete testosterone and the ovaries secrete oestrogen and progesterone, which control secondary sexual characteristics and reproductive cycles.
(a) Name the disease caused by the deficiency of iodine in our diet and mention its chief physical symptom.(b) State two secondary sexual characteristics induced by testosterone in adolescent boys.
(c) Explain why the adrenal gland is commonly referred to as the “emergency gland” of the body.
OR
What is the role of progesterone secreted by the ovaries in the female reproductive cycle?
Q15.(a) Draw a neat labelled diagram of the human heart showing all four chambers, associated valves, and major blood vessels.
(b) Trace the complete path of a red blood cell as it travels from the right atrium to the aorta during double circulation.
(c) Why is blood pressure significantly higher in systemic arteries than in veins?[5]
(b) Explain the sequence of reproductive events in an angiosperm from pollination to seed and fruit formation.
(c) State one difference between a unisexual flower and a bisexual flower, giving one example of each.
(b) Trace the complete path of a red blood cell as it travels from the right atrium to the aorta during double circulation.
(c) Why is blood pressure significantly higher in systemic arteries than in veins?[5]
OR
(a) Draw a neat diagram of the longitudinal section of a mature pistil/carpel showing pollen germination on the stigma and the path of the pollen tube.(b) Explain the sequence of reproductive events in an angiosperm from pollination to seed and fruit formation.
(c) State one difference between a unisexual flower and a bisexual flower, giving one example of each.
SECTION B – CHEMISTRY
Q16.
When solid copper(II) carbonate is heated strongly in a dry test tube, it turns black and releases a gas that turns limewater milky. The reaction is an example of:[1]
Q17.
A drop of liquid turns red litmus blue and phenolphthalein pink. The pH of this liquid is likely to be:[1]
Q18.
Which of the following non-metals possesses a brilliant metallic lustre?[1]
Q20.
When sulphur dioxide gas ($SO_2$) is passed through an acidified solution of potassium dichromate ($K_2Cr_2O_7$), the colour changes from:[1]
Q21.Assertion (A):
Silver articles develop a black tarnished coating when left exposed to ambient air for several days.
Reason (R): Silver reacts with trace amounts of hydrogen sulphide ($H_2S$) gas in air to form a thin black layer of silver sulphide ($Ag_2S$).[1]
Reason (R): Silver reacts with trace amounts of hydrogen sulphide ($H_2S$) gas in air to form a thin black layer of silver sulphide ($Ag_2S$).[1]
Q22.
State what you would observe when a piece of clean zinc strip is placed into an aqueous solution of copper sulphate. Write the balanced chemical equation.[2]
Q23.
Explain the extraction of mercury from its sulphide ore (cinnabar, $HgS$). Write balanced chemical equations for all steps involved.[3]
(b) Why are carbon reduction methods unsuitable for extracting metals high in the reactivity series like magnesium and calcium?
OR
(a) Define the term calcination. Give one balanced chemical equation for the calcination of zinc carbonate.(b) Why are carbon reduction methods unsuitable for extracting metals high in the reactivity series like magnesium and calcium?
Q24.(a) Draw the structural formulas and electron dot structures of:
(i) Methanol ($CH_3OH$) (ii) Ethanal ($CH_3CHO$)
(b) Explain why diamond is extremely hard with a high melting point, whereas graphite is soft and conducts electricity.[3]
(i) Methanol ($CH_3OH$) (ii) Ethanal ($CH_3CHO$)
(b) Explain why diamond is extremely hard with a high melting point, whereas graphite is soft and conducts electricity.[3]
Q25. Read the following passage and answer the questions:[4]
(b) Name the two chemical ions present in hard water that cause permanent hardness.
(c) Explain how washing soda removes the permanent hardness of water. Write the chemical reaction involved.
OR
Differentiate between baking soda and baking powder with respect to their chemical compositions.
When washing soda ($Na_2CO_3 \cdot 10H_2O$) crystals are left exposed to dry air, they lose nine molecules of water of crystallisation to form a white monohydrate powder ($Na_2CO_3 \cdot H_2O$). This property is known as efflorescence. Washing soda is prepared commercially from sodium chloride through the Solvay process and is widely used in laundry, glass manufacturing, and for removing the permanent hardness of water caused by dissolved calcium and magnesium sulphates and chlorides.
(a) What is efflorescence? Write the chemical equation for the efflorescence of washing soda crystals.(b) Name the two chemical ions present in hard water that cause permanent hardness.
(c) Explain how washing soda removes the permanent hardness of water. Write the chemical reaction involved.
OR
Differentiate between baking soda and baking powder with respect to their chemical compositions.
Q26.(a) What is an esterification reaction? Write a balanced chemical equation for the reaction between ethanoic acid and ethanol in the presence of concentrated sulphuric acid.
(b) State the physical property of esters that makes them useful in perfumes and flavouring agents.
(c) How can ethanoic acid be recovered from an ester? Name the reaction and write the equation.[5]
(b) Write a balanced chemical equation for the chlor-alkali process.
(c) State the gas collected at:
(i) The Anode (ii) The Cathode
(d) Mention one major industrial application for each of the three products obtained from this process.
(b) State the physical property of esters that makes them useful in perfumes and flavouring agents.
(c) How can ethanoic acid be recovered from an ester? Name the reaction and write the equation.[5]
OR
(a) What is the chlor-alkali process? Why is it given this name?(b) Write a balanced chemical equation for the chlor-alkali process.
(c) State the gas collected at:
(i) The Anode (ii) The Cathode
(d) Mention one major industrial application for each of the three products obtained from this process.
Q27.
What is an amphoteric oxide? Give two balanced chemical equations to prove that aluminium oxide ($Al_2O_3$) is an amphoteric oxide.[2]
SECTION C – PHYSICS
Q28.
A spherical mirror produces a virtual, erect, and magnified image of an object. The mirror must be:[1]
Q29.
The splitting of white light into its component spectral colours when passing through a prism is called:[1]
Q30.
Two wires of the same material and same length have radii in the ratio $1 : 2$. The ratio of their electrical resistances ($R_1 : R_2$) is:[1]
Q31.
The magnetic field produced inside a long straight solenoid carrying steady direct current depends directly upon:[1]
Q32.Assertion (A):
A concave lens is used in spectacles prescribed for a person suffering from myopia (near-sightedness).
Reason (R): A concave lens diverges incoming light rays, shifting the focused image backwards onto the retina.[1]
Reason (R): A concave lens diverges incoming light rays, shifting the focused image backwards onto the retina.[1]
Q33.Assertion (A):
The commercial unit of electrical energy ($1\text{ kWh}$) is equal to $3.6 \times 10^6\text{ Joules}$.
Reason (R): $1\text{ kWh}$ represents the total energy consumed by a device of 1000 watts operating continuously for 1 hour.[1]
Reason (R): $1\text{ kWh}$ represents the total energy consumed by a device of 1000 watts operating continuously for 1 hour.[1]
Q34.
An object is placed at a distance of 10 cm in front of a convex lens of focal length 15 cm. Find the position, nature, and magnification of the image formed using the lens formula.[2]
Q35.
A current of 4 A flows through an electric toaster connected to a 220 V line for 2 minutes. Calculate the electrical energy consumed in joules.[2]
OR
State Ohm’s law and sketch a V-I graph for an ohmic metallic conductor at constant temperature.Q36.(a) What is meant by the persistence of vision of the human eye?
(b) Why does the Sun appear elliptical or flattened at sunrise and sunset?
(c) State why astronauts in outer space observe stars without any twinkling effect.[3]
(b) Why does the Sun appear elliptical or flattened at sunrise and sunset?
(c) State why astronauts in outer space observe stars without any twinkling effect.[3]
Q37.
Explain the working principle and structural role of each of the following components in a simple DC electric motor:
(a) Armature coil (b) Split-ring commutator (c) Carbon brushes[3]
(a) Armature coil (b) Split-ring commutator (c) Carbon brushes[3]
Q38. Read the following passage and answer the questions:[4]
(b) State two functional advantages of connecting household electrical appliances in parallel rather than in series.
(c) What is an electric fuse? On what physical law does its operation depend?
OR
An electric geyser rated at $1500\text{ W}$ operates for 2 hours daily. Calculate the cost of electricity consumed in a 30-day month at the rate of ₹6.00 per unit (kWh).
Domestic electrical wiring supplies alternating current (AC) at 220 V and 50 Hz in India. Appliances are wired in parallel across the live and neutral wires. Two separate circuits are installed: a 15 A power circuit for heavy appliances (air conditioners, geysers) and a 5 A lighting circuit for bulbs and fans. Proper earthing ensures that metallic casings remain at ground potential (0 V), protecting users from electrical shocks in the event of insulation failure.
(a) What is the frequency and voltage of domestic AC electric power supplied in India?(b) State two functional advantages of connecting household electrical appliances in parallel rather than in series.
(c) What is an electric fuse? On what physical law does its operation depend?
OR
An electric geyser rated at $1500\text{ W}$ operates for 2 hours daily. Calculate the cost of electricity consumed in a 30-day month at the rate of ₹6.00 per unit (kWh).
Q39.(a) State the laws of refraction of light and write Snell’s law formula.
(b) A ray of light travelling in water ($n = 1.33$) strikes the surface of a dense flint glass plate ($n = 1.65$). Calculate the refractive index of glass with respect to water.
(c) Define the critical angle and total internal reflection with the help of a neat labelled ray diagram.[5]
(b) A straight conductor carrying a current of 5 A is placed perpendicular to a uniform magnetic field of strength 0.2 T. If the length of the conductor inside the field is 0.5 m, calculate the mechanical force acting on it.
(c) State two practical methods to increase the strength of an electromagnet.
(b) A ray of light travelling in water ($n = 1.33$) strikes the surface of a dense flint glass plate ($n = 1.65$). Calculate the refractive index of glass with respect to water.
(c) Define the critical angle and total internal reflection with the help of a neat labelled ray diagram.[5]
OR
(a) Draw the magnetic field lines surrounding a current-carrying straight conductor. State the rule used to determine their direction.(b) A straight conductor carrying a current of 5 A is placed perpendicular to a uniform magnetic field of strength 0.2 T. If the length of the conductor inside the field is 0.5 m, calculate the mechanical force acting on it.
(c) State two practical methods to increase the strength of an electromagnet.
CBSE CLASS X SCIENCE – COMPLETE SOLUTIONS & MARKING SCHEME (SET – 10)
SECTION A – BIOLOGY SOLUTIONS
Q1. (b) Chloroplast [1 Mark]
Explanation: The light-dependent reactions of photosynthesis take place in the thylakoid membranes/grana of the chloroplasts, where chlorophyll pigments absorb solar radiation.
Explanation: The light-dependent reactions of photosynthesis take place in the thylakoid membranes/grana of the chloroplasts, where chlorophyll pigments absorb solar radiation.
Q2. (c) Medulla oblongata [1 Mark]
Explanation: The medulla oblongata in the hindbrain houses vital autonomic reflex centres for coughing, sneezing, swallowing, vomiting, and salivation.
Explanation: The medulla oblongata in the hindbrain houses vital autonomic reflex centres for coughing, sneezing, swallowing, vomiting, and salivation.
Q3. (b) Leishmania [1 Mark]
Explanation: Leishmania (the protozoan pathogen of Kala-azar) has a whip-like flagellum at one end and reproduces by binary fission in a fixed longitudinal orientation relative to this structure.
Explanation: Leishmania (the protozoan pathogen of Kala-azar) has a whip-like flagellum at one end and reproduces by binary fission in a fixed longitudinal orientation relative to this structure.
Q4. (a) Female child [1 Mark]
Explanation: The ovum always contributes an X chromosome ($22+X$). Fertilisation by an X-bearing sperm ($22+X$) produces a female zygote ($44+XX$).
Explanation: The ovum always contributes an X chromosome ($22+X$). Fertilisation by an X-bearing sperm ($22+X$) produces a female zygote ($44+XX$).
Q5. (b) Polyethylene plastic [1 Mark]
Explanation: Synthetic polymers such as polyethylene cannot be degraded by bacterial or fungal enzymes, resulting in long-term environmental accumulation and microplastic contamination.
Explanation: Synthetic polymers such as polyethylene cannot be degraded by bacterial or fungal enzymes, resulting in long-term environmental accumulation and microplastic contamination.
Q6. (a) Grasshopper and Zooplankton [1 Mark]
Explanation: Primary consumers are herbivores that feed directly on producers. In terrestrial systems, grasshoppers feed on grass; in aquatic systems, zooplankton feed on phytoplankton.
Explanation: Primary consumers are herbivores that feed directly on producers. In terrestrial systems, grasshoppers feed on grass; in aquatic systems, zooplankton feed on phytoplankton.
Q7. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Blood platelets aggregate at injury sites and release thromboplastin, initiating the enzymatic conversion of fibrinogen into an insoluble fibrin mesh that seals wounds and prevents haemorrhage.
Explanation: Blood platelets aggregate at injury sites and release thromboplastin, initiating the enzymatic conversion of fibrinogen into an insoluble fibrin mesh that seals wounds and prevents haemorrhage.
Q8. (c) A is true but R is false. [1 Mark]
Explanation: Pesticides like DDT are non-biodegradable and cannot be excreted or metabolised. As a result, their concentration increases at each successive trophic level (biomagnification), reaching maximum concentration in top consumers.
Explanation: Pesticides like DDT are non-biodegradable and cannot be excreted or metabolised. As a result, their concentration increases at each successive trophic level (biomagnification), reaching maximum concentration in top consumers.
Q9. Sweet Taste of Chewed Bread: [2 Marks]
- Bread contains complex, tasteless starch molecules. [1 Mark]
- Chewing mixes the bread with saliva containing the enzyme salivary amylase, which breaks down starch into sweet-tasting disaccharides like maltose: $\text{Starch} \xrightarrow{\text{Salivary Amylase}} \text{Maltose (sugar)}$. [1 Mark]
Q10. Binary Fission in Amoeba vs Budding in Yeast: [2 Marks]
| Feature | Binary Fission in Amoeba | Budding in Yeast |
|---|---|---|
| Division Equality | Parent cell divides symmetrically into two equal-sized daughter cells. [1 Mark] | Parent cell undergoes unequal division, forming a small outgrowth (bud). |
| Parent Identity | Parent cell body splits completely; parent identity is lost. [1 Mark] | Parent cell retains its identity while the bud detaches or forms chains. |
Q11. Thigmotropism and Tendril Coiling: [3 Marks]
- (a) Thigmotropism: The directional growth movement of a plant organ in response to mechanical touch/physical contact. Example: Tendrils of pea or passiflora. [1 Mark]
- (b) Mechanism: When a tendril touches a support, auxins diffuse away from the side in contact towards the side away from the contact. The higher auxin concentration accelerates cell elongation on the outer side, causing the tendril to curve and coil tightly around the support. [1.5 Marks]
- (c) Ethylene is the gaseous phytohormone responsible for fruit ripening. [0.5 Mark]
Q12. Monohybrid Cross on Flower Colour: [3 Marks]
- (a) F₁ Generation: All offspring will have Violet flowers (Genotype: $Vv$). [1 Mark]
- (b) F₂ Generation Selfing ($Vv \times Vv$): Produces genotypes $1\ VV : 2\ Vv : 1\ vv$. White-flowered plants ($vv$) account for 1 out of 4 offspring, which equals 25%. [1 Mark]
- (c) Ratios:
- Phenotypic Ratio = 3 Violet : 1 White. [0.5 Mark]
- Genotypic Ratio = 1 $VV$ : 2 $Vv$ : 1 $vv$ (1 : 2 : 1). [0.5 Mark]
Q13. Stomata Structure and Regulation: [3 Marks]
- Definition: Stomata are microscopic pores present in the epidermis of leaves and young green stems. [0.5 Mark]
- Functions: (i) Mediate gaseous exchange ($CO_2$ intake and $O_2$ release) during photosynthesis and respiration; (ii) Regulate transpiration, providing evaporative cooling and transpiration pull for sap ascent. [1 Mark]
- Guard Cell Action: Guard cells swell and become turgid when water enters them, causing their outer thin walls to stretch outward and pulling the inner thick walls apart to open the pore. When guard cells lose water, they become flaccid, causing the pore to close. [1.5 Marks]
Q14. Case-Based Solutions (Biology): [4 Marks]
- (a) Disease: Goitre; Symptom: Swollen neck caused by an enlarged thyroid gland. [1 Mark]
- (b) Secondary sexual characteristics: (i) Deepening of the voice due to enlargement of the larynx; (ii) Growth of facial, axillary, and pubic hair; (iii) Broadening of shoulders and increased muscle mass. (Any two) [1.5 Marks]
- (c) Adrenaline increases heart rate, elevates systolic blood pressure, accelerates breathing rate, and stimulates hepatic glycogenolysis, quickly supplying oxygen and glucose to skeletal muscles during fight-or-flight emergencies. [1.5 Marks]
- Progesterone thickens and vascularises the endometrium of the uterus, preparing it for blastocyst implantation and supporting pregnancy. It also inhibits uterine contractions during gestation. [2 Marks]
Q15. Long Answer (Biology): [5 Marks]
- (a) Heart Diagram: Diagram showing the Right Atrium, Right Ventricle, Left Atrium, Left Ventricle, Tricuspid/Bicuspid valves, Septum, Superior/Inferior Vena Cava, Pulmonary Artery, Pulmonary Veins, and Aorta. [2 Marks]
- (b) Path of RBC:
- Right Atrium $\rightarrow$ Tricuspid Valve $\rightarrow$ Right Ventricle. [0.5 Mark]
- Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Pulmonary Capillaries of Lungs (Oxygenation). [0.5 Mark]
- Pulmonary Veins $\rightarrow$ Left Atrium $\rightarrow$ Bicuspid (Mitral) Valve $\rightarrow$ Left Ventricle. [0.5 Mark]
- Left Ventricle $\rightarrow$ Aortic Valve $\rightarrow$ Systemic Aorta $\rightarrow$ Body tissues. [0.5 Mark]
- (c) Systemic arteries receive blood pumped directly from the left ventricle under high systolic pressure, whereas veins collect blood after it has passed through narrow capillary networks where fluid pressure drops. [1 Mark]
- (a) Pistil Diagram: Labelled drawing showing Stigma, Style, Ovary, Ovule, Pollen grain germinating with Pollen tube, Female Gametophyte (Embryo sac), and Micropyle. [2 Marks]
- (b) Reproductive Events:
- Pollination: Transfer of pollen grains from an anther to the stigma. [0.5 Mark]
- Pollen tube growth: A pollen tube germinates and grows down through the style carrying two male gametes into the ovule. [0.5 Mark]
- Double Fertilisation: One male gamete fertilises the egg cell to form a diploid zygote (syngamy), while the second male gamete fuses with the two polar nuclei to form the triploid endosperm (triple fusion). [1 Mark]
- (c) Unisexual Flower: Contains either stamens or carpels (e.g., Papaya, Watermelon). Bisexual Flower: Contains both stamens and carpels in the same flower (e.g., Hibiscus, Mustard). [1 Mark]
SECTION B – CHEMISTRY SOLUTIONS
Q16. (a) Thermal decomposition [1 Mark]
Explanation: Copper carbonate decomposes upon heating into black copper(II) oxide and carbon dioxide: $CuCO_3(s) \xrightarrow{\Delta} CuO(s) + CO_2(g)\uparrow$.
Explanation: Copper carbonate decomposes upon heating into black copper(II) oxide and carbon dioxide: $CuCO_3(s) \xrightarrow{\Delta} CuO(s) + CO_2(g)\uparrow$.
Q17. (d) 10 [1 Mark]
Explanation: Turning red litmus blue and phenolphthalein pink indicates a basic (alkaline) solution, which corresponds to a $\text{pH} > 7$ (such as $\text{pH} = 10$).
Explanation: Turning red litmus blue and phenolphthalein pink indicates a basic (alkaline) solution, which corresponds to a $\text{pH} > 7$ (such as $\text{pH} = 10$).
Q18. (c) Iodine [1 Mark]
Explanation: Iodine is a dark violet-black non-metallic solid that displays a distinct metallic lustre.
Explanation: Iodine is a dark violet-black non-metallic solid that displays a distinct metallic lustre.
Q19. (b) Ester (–COOR) [1 Mark]
Explanation: Ethyl ethanoate ($CH_3COOCH_2CH_3$) contains the ester functional group ($-COO-$).
Explanation: Ethyl ethanoate ($CH_3COOCH_2CH_3$) contains the ester functional group ($-COO-$).
Q20. (a) Orange to green [1 Mark]
Explanation: Sulphur dioxide reduces orange dichromate ions ($Cr_2O_7^{2-}$) to green chromium ions ($Cr^{3+}$): $K_2Cr_2O_7 + H_2SO_4 + 3SO_2 \rightarrow K_2SO_4 + Cr_2(SO_4)_3\text{ (green)} + H_2O$.
Explanation: Sulphur dioxide reduces orange dichromate ions ($Cr_2O_7^{2-}$) to green chromium ions ($Cr^{3+}$): $K_2Cr_2O_7 + H_2SO_4 + 3SO_2 \rightarrow K_2SO_4 + Cr_2(SO_4)_3\text{ (green)} + H_2O$.
Q21. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: Atmospheric $H_2S$ reacts slowly with metallic silver surfaces to form a thin adherent layer of black silver sulphide ($2Ag + H_2S \rightarrow Ag_2S + H_2$).
Explanation: Atmospheric $H_2S$ reacts slowly with metallic silver surfaces to form a thin adherent layer of black silver sulphide ($2Ag + H_2S \rightarrow Ag_2S + H_2$).
Q22. Zinc with Copper Sulphate: [2 Marks]
- Observations: The blue colour of the copper sulphate solution gradually fades until it becomes colourless, and a reddish-brown coating of copper metal deposits on the zinc strip. [1 Mark]
- Equation: $Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$ [1 Mark]
Q23. Extraction of Mercury from Cinnabar: [3 Marks]
- Roasting: Cinnabar ore ($HgS$) is heated in air to convert it into mercuric oxide:
$2HgS(s) + 3O_2(g) \xrightarrow{\Delta} 2HgO(s) + 2SO_2(g)\uparrow$ [1.5 Marks] - Thermal Reduction: Mercuric oxide is unstable at high temperatures and decomposes upon further heating to yield liquid mercury metal:
$2HgO(s) \xrightarrow{\Delta > 300^\circ\text{C}} 2Hg(l) + O_2(g)\uparrow$ [1.5 Marks]
- (a) Calcination: The process of heating a carbonate or hydrated ore strongly below its melting point in limited or no air.
$ZnCO_3(s) \xrightarrow{\Delta} ZnO(s) + CO_2(g)\uparrow$ [1.5 Marks] - (b) Metals high in the reactivity series (Mg, Ca, Na, Al) have a stronger affinity for oxygen than carbon does, so carbon cannot reduce their oxides. They are extracted instead via electrolytic reduction of their molten chlorides or oxides. [1.5 Marks]
Q24. Structures and Allotropes of Carbon: [3 Marks]
- (a) Structures:
- (i) Methanol ($CH_3OH$): Carbon bonded to three hydrogen atoms and one hydroxyl ($-OH$) group. [0.75 Mark]
- (ii) Ethanal ($CH_3CHO$): A methyl group ($-CH_3$) single-bonded to a formyl carbon with a double-bonded oxygen and single-bonded hydrogen ($H-C(=O)-$). [0.75 Mark]
- (b) Diamond vs Graphite:
- Diamond: Each carbon is covalently bonded to four other carbon atoms in a rigid, three-dimensional tetrahedral network, resulting in high hardness and melting point. [0.75 Mark]
- Graphite: Each carbon is bonded to three other carbons in planar hexagonal layers held by weak van der Waals forces (allowing layers to slide). It has one free delocalised valence electron per carbon, allowing it to conduct electricity. [0.75 Mark]
Q25. Case-Based Solutions (Chemistry): [4 Marks]
- (a) Efflorescence: The spontaneous loss of water of crystallisation from a hydrated salt when exposed to dry air.
$Na_2CO_3 \cdot 10H_2O(s) \xrightarrow{\text{dry air}} Na_2CO_3 \cdot H_2O(s) + 9H_2O(g)$ [1.5 Marks] - (b) Calcium ions ($Ca^{2+}$) and Magnesium ions ($Mg^{2+}$) (as dissolved sulphates or chlorides). [1 Mark]
- (c) Sodium carbonate precipitates dissolved $Ca^{2+}$ and $Mg^{2+}$ ions as insoluble carbonates, removing them from solution:
$CaSO_4(aq) + Na_2CO_3(aq) \rightarrow CaCO_3(s)\downarrow + Na_2SO_4(aq)$ [1.5 Marks]
- Baking Soda: Pure chemical compound, Sodium hydrogen carbonate ($NaHCO_3$). [1 Mark]
- Baking Powder: A dry solid mixture containing baking soda ($NaHCO_3$) and an edible acid like tartaric acid (along with starch filler), which prevents an alkaline bitter taste by neutralising the $Na_2CO_3$ formed during baking. [1 Mark]
Q26. Long Answer (Chemistry): [5 Marks]
- (a) Esterification: The condensation reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst to form a sweet-smelling ester and water.
$CH_3COOH + C_2H_5OH \xrightarrow{\text{conc. } H_2SO_4} CH_3COOC_2H_5\text{ (Ethyl ethanoate)} + H_2O$ [2 Marks] - (b) Esters possess pleasant, sweet, fruity fragrances. [1 Mark]
- (c) Saponification / Alkaline Hydrolysis: Treating the ester with dilute $NaOH$ yields sodium ethanoate and ethanol, which can then be acidified with $HCl$ to regenerate ethanoic acid:
$CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH$
$CH_3COONa + HCl \rightarrow CH_3COOH + NaCl$ [2 Marks]
- (a) Chlor-Alkali Process: The electrolysis of cold, concentrated aqueous sodium chloride (brine). Named “chlor-alkali” for its two primary products: chlor for chlorine gas and alkali for sodium hydroxide. [1.5 Marks]
- (b) Equation: $2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{electrolysis}} 2NaOH(aq) + Cl_2(g)\uparrow + H_2(g)\uparrow$ [1.5 Marks]
- (c) Anode (+): Chlorine gas ($Cl_2$); Cathode (–): Hydrogen gas ($H_2$). [1 Mark]
- (d) Uses: (i) $NaOH$: Soap manufacturing and paper making; (ii) $Cl_2$: Water disinfection and PVC production; (iii) $H_2$: Hydrogenation of vegetable oils and production of ammonia for fertilisers. [1 Mark]
Q27. Amphoteric Oxides: [2 Marks]
- Definition: Metallic oxides that react with both acids and bases to produce salt and water. [1 Mark]
- Equations with $Al_2O_3$:
- With Acid: $Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O$ [0.5 Mark]
- With Base: $Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2\text{ (Sodium aluminate)} + H_2O$ [0.5 Mark]
SECTION C – PHYSICS SOLUTIONS
Q28. (c) Concave mirror [1 Mark]
Explanation: When an object is placed between the pole ($P$) and principal focus ($F$) of a concave mirror, it forms a virtual, erect, and magnified image behind the mirror. Convex mirrors always form diminished virtual images.
Explanation: When an object is placed between the pole ($P$) and principal focus ($F$) of a concave mirror, it forms a virtual, erect, and magnified image behind the mirror. Convex mirrors always form diminished virtual images.
Q29. (b) Dispersion [1 Mark]
Explanation: The separation of composite white light into its constituent spectral colours through a refracting medium is known as dispersion.
Explanation: The separation of composite white light into its constituent spectral colours through a refracting medium is known as dispersion.
Q30. (c) 4 : 1 [1 Mark]
Explanation: $R = \rho \frac{l}{\pi r^2} \implies R \propto \frac{1}{r^2}$. Given $r_1 : r_2 = 1 : 2$, the resistance ratio is $\frac{R_1}{R_2} = \left(\frac{r_2}{r_1}\right)^2 = \left(\frac{2}{1}\right)^2 = \frac{4}{1}$.
Explanation: $R = \rho \frac{l}{\pi r^2} \implies R \propto \frac{1}{r^2}$. Given $r_1 : r_2 = 1 : 2$, the resistance ratio is $\frac{R_1}{R_2} = \left(\frac{r_2}{r_1}\right)^2 = \left(\frac{2}{1}\right)^2 = \frac{4}{1}$.
Q31. (a) Current and number of turns per unit length [1 Mark]
Explanation: The axial magnetic field inside an ideal solenoid is given by $B = \mu_0 n I$, where $n$ is the number of turns per unit length and $I$ is the electric current.
Explanation: The axial magnetic field inside an ideal solenoid is given by $B = \mu_0 n I$, where $n$ is the number of turns per unit length and $I$ is the electric current.
Q32. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: A myopic eye focuses rays in front of the retina. A diverging (concave) lens provides the necessary divergence to move the focal point back onto the retina.
Explanation: A myopic eye focuses rays in front of the retina. A diverging (concave) lens provides the necessary divergence to move the focal point back onto the retina.
Q33. (a) Both A and R are true and R is the correct explanation of A. [1 Mark]
Explanation: $1\text{ kWh} = 1000\text{ W} \times 3600\text{ s} = 3.6 \times 10^6\text{ J}$. Both assertion and reason are factually correct, with the reason directly defining the unit.
Explanation: $1\text{ kWh} = 1000\text{ W} \times 3600\text{ s} = 3.6 \times 10^6\text{ J}$. Both assertion and reason are factually correct, with the reason directly defining the unit.
Q34. Convex Lens Numerical: [2 Marks]
Given: $f = +15\text{ cm}$, $u = -10\text{ cm}$.
Using Lens Formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} + \frac{1}{u}$
$\frac{1}{v} = \frac{1}{15} + \frac{1}{-10} = \frac{2 – 3}{30} = -\frac{1}{30} \implies v = \mathbf{-30\text{ cm}}$. [1 Mark]
Magnification: $m = \frac{v}{u} = \frac{-30}{-10} = \mathbf{+3}$.
Nature: Virtual, erect, and magnified (3 times), formed at $30\text{ cm}$ on the same side as the object. [1 Mark]
Given: $f = +15\text{ cm}$, $u = -10\text{ cm}$.
Using Lens Formula: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} + \frac{1}{u}$
$\frac{1}{v} = \frac{1}{15} + \frac{1}{-10} = \frac{2 – 3}{30} = -\frac{1}{30} \implies v = \mathbf{-30\text{ cm}}$. [1 Mark]
Magnification: $m = \frac{v}{u} = \frac{-30}{-10} = \mathbf{+3}$.
Nature: Virtual, erect, and magnified (3 times), formed at $30\text{ cm}$ on the same side as the object. [1 Mark]
Q35. Energy Consumed Calculation: [2 Marks]
Given: $I = 4\text{ A}$, $V = 220\text{ V}$, $t = 2\text{ min} = 2 \times 60 = 120\text{ s}$.
Energy $E = V \times I \times t$ [1 Mark]
$E = 220\text{ V} \times 4\text{ A} \times 120\text{ s} = \mathbf{105,600\text{ J}}$ (or $105.6\text{ kJ}$). [1 Mark]
OR
Ohm’s Law: At constant temperature, the current ($I$) flowing through a metallic conductor is directly proportional to the potential difference ($V$) across its ends ($V \propto I \implies V = I R$). The V-I graph is a straight line passing through the origin. [2 Marks]
Given: $I = 4\text{ A}$, $V = 220\text{ V}$, $t = 2\text{ min} = 2 \times 60 = 120\text{ s}$.
Energy $E = V \times I \times t$ [1 Mark]
$E = 220\text{ V} \times 4\text{ A} \times 120\text{ s} = \mathbf{105,600\text{ J}}$ (or $105.6\text{ kJ}$). [1 Mark]
OR
Ohm’s Law: At constant temperature, the current ($I$) flowing through a metallic conductor is directly proportional to the potential difference ($V$) across its ends ($V \propto I \implies V = I R$). The V-I graph is a straight line passing through the origin. [2 Marks]
Q36. Optical Phenomena: [3 Marks]
- (a) Persistence of Vision: The visual impression of an image remains on the retina for about $\frac{1}{16}\text{th}$ of a second after the light stimulus ceases, allowing sequential still frames to appear as continuous motion. [1 Mark]
- (b) Apparent Flattening of the Sun: Light rays from the lower edge of the solar disc pass through denser air layers than rays from the upper edge, undergoing greater upward atmospheric refraction. This differential refraction compresses the vertical diameter, making the Sun appear elliptical. [1 Mark]
- (c) Outer space lacks an atmosphere, eliminating atmospheric turbulence and refractive index variations. As a result, starlight travels along straight paths without flickering. [1 Mark]
Q37. Components of a DC Motor: [3 Marks]
- Working Principle: Converts electrical energy into mechanical rotational energy based on the principle that a current-carrying coil in a magnetic field experiences a deflecting mechanical torque (governed by Fleming’s Left-Hand Rule). [1 Mark]
- (a) Armature coil: A soft iron core wrapped with insulated copper wire that produces a magnetic field to generate continuous rotational torque. [0.75 Mark]
- (b) Split-ring commutator: Reverses the direction of current in the coil halves every half rotation to ensure unidirectional rotation. [0.75 Mark]
- (c) Carbon brushes: Flexible conductive contacts that press against rotating commutator segments to deliver direct current from the external power supply without tangling wires. [0.5 Mark]
Q38. Case-Based Solutions (Physics): [4 Marks]
- (a) Voltage: 220 V; Frequency: 50 Hz (alternates direction 100 times per second). [1 Mark]
- (b) Advantages of Parallel Wiring: (i) Each appliance receives the full mains voltage (220 V); (ii) Each appliance can be switched on/off independently without affecting others. [1 Mark]
- (c) An electric fuse is a safety device containing a low-melting-point alloy wire. It operates on Joule’s Law of Heating ($H = I^2 R t$), melting to break the circuit during overcurrent or short circuits. [2 Marks]
- Power $P = 1500\text{ W} = 1.5\text{ kW}$, Time per day $t = 2\text{ h}$.
Daily energy consumed $= 1.5\text{ kW} \times 2\text{ h} = 3.0\text{ kWh}$ (units/day).
Monthly energy consumed (30 days) $= 3.0 \times 30 = \mathbf{90\text{ kWh}}$. [1 Mark]
Total Cost $= 90\text{ units} \times ₹6.00/\text{unit} = \mathbf{₹540.00}$. [1 Mark]
Q39. Long Answer (Physics): [5 Marks]
- (a) Laws of Refraction:
- The incident ray, refracted ray, and 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 a given pair of media: $\frac{\sin i}{\sin r} = n_{21}$. [1 Mark]
- (b) Relative refractive index: $^{w}n_g = \frac{n_g}{n_w} = \frac{1.65}{1.33} \approx \mathbf{1.24}$. [1 Mark]
- (c) Critical Angle and TIR: The critical angle ($i_c$) is the angle of incidence in an optically denser medium for which the angle of refraction in the rarer medium is $90^\circ$. When the angle of incidence exceeds the critical angle, the ray is reflected back into the denser medium (Total Internal Reflection). (Accompanying diagram). [2 Marks]
- (a) Magnetic Field of Straight Conductor: Concentric circular loops centered on the wire. The direction is determined using the Right-Hand Thumb Rule: if the thumb points in the direction of current, curled fingers indicate the direction of the magnetic field lines. [2 Marks]
- (b) Force Calculation:
Given: $I = 5\text{ A}$, $B = 0.2\text{ T}$, $L = 0.5\text{ m}$, $\theta = 90^\circ$.
$F = B I L \sin 90^\circ = 0.2\text{ T} \times 5\text{ A} \times 0.5\text{ m} \times 1 = \mathbf{0.5\text{ N}}$. [1.5 Marks] - (c) Methods to increase electromagnet strength: (i) Increase the magnitude of electric current flowing through the coil; (ii) Increase the number of turns of the solenoid coil. [1.5 Marks]