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CLASS 10 CBSE SCIENCE
Section A: Assertion and Reasoning (Q1–20)
Instructions: For questions 1 to 20, two statements are given—Assertion (A) and Reason (R). Select the correct option:
- a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation.
- b) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation.
- c) Assertion (A) is true but Reason (R) is false.
- d) Assertion (A) is false but Reason (R) is true.
Q1. Assertion The centre of curvature is not a part of the mirror.
Reason: The reflecting surface of a spherical mirror is a part of a sphere which has a centre.
Q2. Assertion A convex mirror is used as a driver’s mirror.
Reason: Convex mirrors have a wider field of view as they are curved outwards and they always form virtual, erect, and diminished images.
Q3.Assertion The refractive index of a medium is a dimensionless quantity.
Reason: The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium.
Q4. Assertion A concave lens will always form a virtual, erect, and diminished image.
Reason: A concave lens is a diverging lens.
Q5. Assertion The power of a convex lens is positive and that of a concave lens is negative.
Reason: Power of a lens is the reciprocal of its focal length.
Q6. Assertion When light travels from a rarer to a denser medium, it bends away from the normal.
Reason: The speed of light is lower in a denser medium.
Q7. Assertion A ray of light passing through the optical centre of a lens emerges without any deviation.
Reason: The optical centre is a point on the principal axis of a lens such that a ray of light passing through it does not suffer any deviation.
Q8. Assertion Alloys are commonly used in electrical heating devices, like electric irons and heaters.
Reason: The resistivity of an alloy is generally higher than that of its constituent metals and they do not oxidize readily at high temperatures.
Q9. Assertion The connecting wires in a circuit are made of copper.
Reason: Copper has very low electrical resistance.
Q10. Assertion In a parallel combination of resistors, the equivalent resistance is less than the least individual resistance.
Reason: In a parallel combination, the total current is divided among the different resistors.
Q11. Assertion A 100 W bulb consumes more electrical energy than a 60 W bulb when operated for the same time at the same voltage.
Reason: Power is the rate of consumption of energy.
Q12. Assertion The SI unit of electric current is Ampere.
Reason: One ampere is constituted by the flow of one coulomb of charge per second.
Q13.Assertion When resistors are connected in series, the current through each resistor is the same.
Reason: The potential difference across each resistor is the same in a series combination.
Q14. Assertion The heating element of an electric heater is made of nichrome.
Reason: Nichrome has a high melting point and high resistivity.
Q15. Assertion Carbon forms a large number of compounds.
Reason: Carbon exhibits the property of catenation and has a valency of four.
Q16. Assertion Soaps are not effective in hard water.
Reason: Soaps form insoluble precipitates (scum) with calcium and magnesium ions present in hard water.
Q17. Assertion Diamond is a good conductor of electricity.
Reason: In diamond, each carbon atom is bonded to four other carbon atoms, leaving no free electrons.
Q18. Assertion Ethanoic acid is a weak acid.
Reason: It ionizes completely in an aqueous solution.
Q19.Assertion Unsaturated hydrocarbons undergo addition reactions.
Reason: Unsaturated hydrocarbons have double or triple bonds between carbon atoms.
Q20. Assertion Butane and 2-methylpropane are isomers.
Reason: Isomers have the same molecular formula but different structural formulas.
CLASS 10 CBSE SCIENCE
Section B: Short Answer Questions (Q21–30)
Q21. Define the principal focus of a concave mirror.
(2 marks)
Q22. State the two laws of reflection of light.
(2 marks)
Q23. Draw a ray diagram to show the formation of an image by a convex lens when the object is placed between F1 and 2F1. State the nature, position, and size of the image formed.
(2 marks)
Q24. What is meant by the power of a lens? What is its SI unit?
(2 marks)
Q25. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
(2 marks)
Q26. Explain why the sky appears blue on a clear day.
(2 marks)
Q27. Differentiate between a real image and a virtual image.
(2 marks)
Q28. What is refractive index? How is it related to the speed of light?
(2 marks)
Q29. A person needs a lens of power -5.5 dioptres for correcting his distant vision. What is the focal length of the lens required? What is the nature of the lens?
(2 marks)
Q30. State Snell’s law of refraction of light.
(2 marks)
CLASS 10 CBSE SCIENCE
Section B: Short Answer Questions (Q31–40)
Q31. Why do we prefer a convex mirror as a rear-view mirror in vehicles?
(2 marks)
Q32. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
(2 marks)
Q33. Define 1 volt. Name a device that helps to maintain a potential difference across a conductor.
(2 marks)
Q34. State Ohm’s law. Draw a V-I graph for an ohmic conductor.
(2 marks)
Q35. What is the heating effect of electric current? Give two applications.
(2 marks)
Q36. Define electrical resistivity. What is its SI unit?
(2 marks)
Q37. On what factors does the resistance of a conductor depend?
(2 marks)
Q38. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
(2 marks)
Q39. Define electric power. Write the mathematical expression for it in terms of V and I.
(2 marks)
Q40. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
(2 marks)
CLASS 10 CBSE SCIENCE
Section B: Short Answer Questions (Q41–53)
Q41. Differentiate between resistance and resistivity.
(2 marks)
Q42. What is an electric fuse? What is its role in electric circuits?
(2 marks)
Q43. What is covalent bonding? Explain with the example of a methane molecule (CH4).
(2 marks)
Q44. Draw the electron dot structure for (i) Ethanoic acid (CH3COOH) and (ii) H2S.
(2 marks)
Q45. What is a homologous series? Write the name and formula of the second member of the alkene series.
(2 marks)
Q46. Differentiate between saturated and unsaturated hydrocarbons.
(2 marks)
Q47. What are isomers? Draw the structures of two isomers of butane (C4H10).
(2 marks)
Q48. Explain the cleansing action of soap.
(2 marks)
Q49. What is an esterification reaction? Write the chemical equation for the reaction.
(2 marks)
Q50. Why does carbon form compounds mainly by covalent bonding?
(2 marks)
Q51. What happens when a piece of sodium metal is added to ethanol? Write the chemical equation for the reaction involved.
(2 marks)
Q52. How is ethanoic acid prepared from ethanol? Name the reaction and write the chemical equation.
(2 marks)
Q53. What are detergents? Why are they more effective in hard water than soaps?
(2 marks)
CLASS 10 CBSE SCIENCE
Section B: Short Answer Questions (Q54–59)
Q54. What is a substitution reaction? Give an example.
(2 marks)
Q55. Explain the versatile nature of carbon.
(2 marks)
Q56. What are functional groups? Give two examples.
(2 marks)
Q57. Why does micelle formation take place when soap is added to water?
(2 marks)
Q58. Write the chemical formula and name of the first member of the alkyne homologous series.
(2 marks)
Q59. What is hydrogenation? What is its industrial application?
(2 marks)
CLASS 10 CBSE SCIENCE
Section C: Numerical Problems (Q61–79)
Q61. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Find the position, size, and nature of the image formed.
(3 marks)
Q62. A concave lens has a focal length of 15 cm. At what distance should the object be placed so that it forms an image at 10 cm from the lens? Also, find the magnification produced by the lens.
(3 marks)
Q63. The refractive index of diamond is 2.42. What is the meaning of this statement? Calculate the speed of light in diamond if the speed of light in air is 3 × 108 m/s.
(3 marks)
Q64. Find the power of a concave lens of focal length 2 m.
(3 marks)
Q65. An object is placed at a distance of 30 cm from a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed to obtain a sharp image? Find the nature and size of the image if the object size is 2 cm.
(3 marks)
Q66. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
(3 marks)
Q67. Light enters from air to a glass plate having a refractive index of 1.50. What is the speed of light in the glass? (Speed of light in vacuum is 3 × 108 m/s).
(3 marks)
Q68. An object of height 4.0 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Find the position and size of the image.
(3 marks)
Q69. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
(3 marks)
Q70. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex mirror of focal length 15 cm. The distance of the object from the mirror is 10 cm. Find the position, nature, and size of the image.
(3 marks)
Q71. An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?
(3 marks)
Q72. Two resistors, with resistances 5 Ω and 10 Ω respectively are to be connected to a battery of emf 6 V so as to obtain: (i) minimum current flowing (ii) maximum current flowing. How will you connect the resistances in each case? Calculate the strength of the total current in each case.
(3 marks)
Q73. An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case?
(3 marks)
Q74. A copper wire has a diameter of 0.5 mm and a resistivity of 1.6 × 10-8 Ω·m. What will be the length of this wire to make its resistance 10 Ω?
(3 marks)
Q75. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 hours.
(3 marks)
Q76. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
(3 marks)
Q77. Calculate the heat produced when 96000 coulombs of charge is transferred in 1 hour through a potential difference of 50 V.
(3 marks)
Q78. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, what will be the power consumed?
(3 marks)
Q79. Find the equivalent resistance when two resistors of resistances R1 = 3 Ω and R2 = 6 Ω are connected in (i) series and (ii) parallel.
(3 marks)
CLASS 10 CBSE SCIENCE
Section D: Case Study Based Questions (Q81–100)
Q81. To get a sharp image on the screen, where should the student place the candle flame?
(1 mark)
Q82. What is the nature of the image formed on the screen?
(1 mark)
Q83. What is the magnification of the image formed?
(1 mark)
Q84. If the student moves the candle flame closer to the lens (e.g., at 15 cm), can he get an image on the screen?
(1 mark)
Q85. What is the power of the lens used by the student?
(1 mark)
Q86. Which bulb will have the highest resistance?
(1 mark)
Q87. What is the total current drawn from the mains when all three bulbs are switched on?
(1 mark)
Q88. Why are the appliances connected in parallel?
(1 mark)
Q89. What is the current drawn by the air conditioner when it is switched on?
(1 mark)
Q90. A fuse with which of the following ratings should be used for the AC circuit?
(1 mark)
Q91. What is the general formula for the alcohol homologous series?
(1 mark)
Q92. What is the IUPAC name of the third member of this series, C3H7OH?
(1 mark)
Q93. When ethanol reacts with hot concentrated sulphuric acid, it forms ethene. What type of reaction is this?
(1 mark)
Q94. Which of the following is a property of ethanol?
(1 mark)
Q95. What is the product formed when ethanol is oxidized using acidified potassium permanganate?
(1 mark)
Q96. The hydrophobic end of a soap molecule is the:
(1 mark)
Q97. The cleansing action of soap is due to the formation of:
(1 mark)
Q98. Why do soaps not work effectively in hard water?
(1 mark)
Q99. Which of the following represents a soap molecule?
(1 mark)
Q100. A structure formed by the aggregation of soap molecules in water is called a micelle. In a micelle:
(1 mark)
CLASS 10 CBSE SCIENCE
Section A: Short Answer Questions (Q101–120)
Q101. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed. Write the chemical equation for the reaction.
(2 marks)
Q102. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Write the chemical equation involved.
(2 marks)
Q103. Identify the substance oxidised and the substance reduced in the following reaction: MnO2 + 4HCl → MnCl2 + 2H2O + Cl2.
(2 marks)
Q104. A solution of a substance ‘X’ is used for whitewashing. Name the substance ‘X’ and write its formula. Write the reaction of the substance ‘X’ with water.
(2 marks)
Q105. What is a redox reaction? Identify the oxidising agent in the reaction: CuO + H2 → Cu + H2O.
(2 marks)
CLASS 10 CBSE SCIENCE
Section B: Assertion and Reasoning (Q121–150)
Q121. Assertion Decomposition of vegetable matter into compost is an example of an exothermic reaction.
Reason: Exothermic reactions are those in which heat is evolved.
Q122. Assertion When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.
Reason: The decomposition reaction takes place on application of heat, therefore, it is an endothermic reaction.
Q123. Assertion In the reaction Fe2O3 + 3CO → 2Fe + 3CO2, carbon monoxide is the reducing agent.
Reason: A substance that helps in oxidation is called a reducing agent.
Q124.Assertion Corrosion of iron is a serious problem.
Reason: Every year a large amount of money is spent to replace damaged iron.
Q125. Assertion In a balanced chemical equation, the total mass of reactants is equal to the total mass of products.
Reason: This is in accordance with the law of conservation of mass.
Q126. Assertion Chips manufacturers usually flush bags of chips with a gas such as nitrogen.
Reason: Nitrogen gas prevents the oil and fats of the chips from being oxidised.
Q127.Assertion Plaster of Paris should be stored in a moisture-proof container.
Reason: Plaster of Paris on coming in contact with moisture absorbs it to form a hard solid mass, gypsum.
Q128. Assertion While diluting an acid, it is recommended that the acid should be added to water and not water to the acid.
Reason: The process of dissolving an acid in water is highly exothermic.
Q129.Assertion The aqueous solutions of glucose and alcohol do not show acidic character.
Reason: Aqueous solutions of glucose and alcohol do not give H+ ions.
Q130. Assertion The pH of a solution of HCl is 2. The pH of this solution will increase on adding some water to it.
Reason: Dilution decreases the H+ ion concentration per unit volume.
Q131.Assertion Weak acids have low electrical conductivity.
Reason: Weak acids dissociate completely in aqueous solution.
Q132.Assertion Baking powder is a mixture of baking soda and a mild edible acid such as tartaric acid.
Reason: The acid neutralises the sodium carbonate formed upon heating, avoiding a bitter taste.
Q133.Assertion Sodium and potassium are stored under kerosene.
Reason: Sodium and potassium are highly reactive metals that react vigorously with oxygen and water.
Q134. Assertion Different metals have different reactivities with water and dilute acids.
Reason: The arrangement of metals in a vertical column in order of decreasing reactivity is called the reactivity series.
Q135.Assertion Ionic compounds have high melting and boiling points.
Reason: A considerable amount of energy is required to break the strong inter-ionic attraction.
Q136. Assertion Zinc oxide is an amphoteric oxide.
Reason: Zinc oxide reacts with both acids and bases to form salt and water.
Q137.Assertion Iron gets rusted in the presence of moist air.
Reason: Rusting is a process of corrosion where iron forms hydrated ferric oxide.
Q138.Assertion Carbon cannot reduce the oxides of sodium or magnesium.
Reason: Sodium and magnesium metals have more affinity for oxygen than carbon.
Q139.Assertion The magnetic field lines around a straight current-carrying conductor are concentric circles.
Reason: The magnetic field strength is directly proportional to the current and inversely proportional to the distance from the conductor.
Q140. Assertion A compass needle placed near a current-carrying wire shows deflection.
Reason: A current-carrying wire produces a magnetic field around it.
Q141.Assertion The magnetic field inside a long straight solenoid carrying current is uniform.
Reason: The magnetic field lines inside the solenoid are in the form of parallel straight lines.
Q142. Assertion An electric motor converts electrical energy into mechanical energy.
Reason: The working of an electric motor is based on the principle of electromagnetic induction.
Q143. Assertion In domestic circuits, appliances are connected in parallel.
Reason: Parallel connection ensures that every appliance gets the same voltage and a fault in one appliance does not affect others.
Q144.Assertion A fuse wire is always connected in series with the live wire.
Reason: A fuse wire has a high melting point.
Q145. The direction of force on a current-carrying conductor in a magnetic field is given by Fleming’s Left-Hand Rule.
Reason: The direction of induced current is given by Fleming’s Right-Hand Rule.
Q146.Assertion No force acts on a current-carrying conductor when it is parallel to the magnetic field.
Reason: The force is maximum when the conductor is perpendicular to the magnetic field.
Q147. Assertion Green-coloured insulation is used for the earth wire.
Reason: The earth wire provides a low-resistance conducting path for the current in case of a fault.
CLASS 10 CBSE SCIENCE
Section C: Case Study 1 (Q151–154)
Context: A student took a small amount of copper oxide in a beaker and added dilute hydrochloric acid to it while stirring. He observed that the colour of the solution became blue-green and the copper oxide dissolved. This is an example of a reaction between a metallic oxide and an acid. Such reactions produce salt and water and are similar to neutralisation reactions. Hence, metallic oxides are said to be basic in nature.
Q151. Write a balanced chemical equation for the reaction between copper oxide and hydrochloric acid.
(1 mark)
Q152. What is the chemical name of the blue-green compound formed?
(1 mark)
Q153. Why are metallic oxides considered basic oxides?
(1 mark)
Q154. What would be observed if a non-metallic oxide like carbon dioxide is reacted with a base like calcium hydroxide?
(1 mark)
CLASS 10 CBSE SCIENCE
Section C: Case Study 2 (Q155–158)
Context: The pH scale is used to measure the acidity or basicity of an aqueous solution. It ranges from 0 to 14. Solutions with a pH less than 7 are acidic, solutions with a pH greater than 7 are basic, and solutions with a pH of 7 are neutral. The pH of a solution is inversely proportional to the concentration of hydrogen ions (H+). Our body works within a narrow pH range of 7.0 to 7.8. Tooth decay starts when the pH of the mouth falls below 5.5.
Q155. A farmer finds the soil in his field has a pH of 4.5. What should he add to the soil to make it suitable for growing crops?
(1 mark)
Q156. How does toothpaste, which is generally basic, help in preventing tooth decay?
(1 mark)
Q157. What is the nature of a solution if its pH is 11? Will it have a high or low concentration of H+ ions?
(1 mark)
Q158. Name the acid produced in our stomach that helps in digestion.
(1 mark)
CLASS 10 CBSE SCIENCE
Section C: Case Study 3 (Q159–162)
Context: The reactivity series is a list of metals arranged in the order of their decreasing chemical activity. Metals at the top are highly reactive and can displace metals below them from their salt solutions. For example, zinc is more reactive than copper, so it displaces copper from copper sulphate solution. This principle is used in various metallurgical processes for the extraction of metals.
Q159. What will you observe when a strip of zinc is placed in a solution of copper sulphate? Write the chemical equation.
(1 mark)
Q160. A metal ‘M’ is found in nature as its sulphide ore (MS). It is used in galvanising iron articles. Identify the metal ‘M’.
(1 mark)
Q161. How is the metal ‘M’ extracted from its sulphide ore? Name the process.
(1 mark)
Q162. Why can’t a solution of copper sulphate be stored in an iron container?
(1 mark)
CLASS 10 CBSE SCIENCE
Section C: Case Studies 4–6 (Q163–174)
Case Study 4 Context: An electric motor is a rotating device that converts electrical energy into mechanical energy. It works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. A simple DC motor consists of a rectangular coil (armature), a strong magnetic field, split-ring commutators, and brushes.
Q163. State the principle on which an electric motor works.
(1 mark)
Q164. What is the function of the split-ring commutator in a DC motor?
(1 mark)
Q165. State the rule used to find the direction of force on the arms of the coil.
(1 mark)
Q166. Suggest two ways to increase the power of a DC motor.
(1 mark)
Case Study 5 Context: When a white powder ‘A’ is heated, it gives a white solid ‘B’ and a colourless, odourless gas ‘C’. The gas ‘C’ turns lime water milky. The solid ‘B’ is used in the manufacturing of cement. The powder ‘A’ is a major component of chalk and marble.
Q167. Identify the white powder ‘A’ and the white solid ‘B’.
(1 mark)
Q168. Identify the gas ‘C’. What is its effect on a burning splinter?
(1 mark)
Q169. Write the balanced chemical equation for the heating of powder ‘A’.
(1 mark)
Q170. What type of chemical reaction is this?
(1 mark)
Case Study 6 Context: Common salt (NaCl) is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, and washing soda. When electricity is passed through brine, it decomposes to form sodium hydroxide. This process is called the chlor-alkali process.
Q171. Write the balanced chemical equation for the chlor-alkali process.
(1 mark)
Q172. Name the gas liberated at the anode during this process. Give one of its uses.
(1 mark)
Q173. What is the common name of the compound CaOCl2 and how is it prepared using a product from the chlor-alkali process?
(1 mark)
Q174. Why is the process named ‘chlor-alkali’?
(1 mark)
CLASS 10 CBSE SCIENCE
Section C: Case Studies 7–10 (Q175–190)
Case Study 7 Context: Metallurgy is the process of extracting metals from their ores and refining them. Highly reactive metals are extracted by electrolysis, moderately reactive metals by reduction with carbon, and least reactive metals are found in native state or require simple heating. Electrolytic refining is common for copper.
Q175. In the electrolytic refining of copper, what is used as the anode and the cathode?
(1 mark)
Q176. What is the electrolyte used in this process?
(1 mark)
Q177. Where do the impurities like silver and gold get collected during the process? What is this collection called?
(1 mark)
Q178. Name a metal that is extracted by the reduction of its oxide with carbon.
(1 mark)
Case Study 8 Context: A solenoid is a long coil of insulated copper wire. When current passes through it, it produces a uniform magnetic field inside. Placing a soft iron core increases the strength, making it an electromagnet.
Q179. What is the nature of magnetic field lines inside a current-carrying solenoid?
(1 mark)
Q180. State two factors on which the strength of the magnetic field produced by a solenoid depends.
(1 mark)
Q181. What is an electromagnet?
(1 mark)
Q182. How is the polarity (North/South poles) at the ends of a current-carrying solenoid determined?
(1 mark)
Case Study 9 Context: A decomposition reaction is when a single compound breaks down into simpler substances. For example, heating ferrous sulphate crystals (FeSO4·7H2O) produces ferric oxide, SO2, and SO3. Silver chloride decomposes in sunlight, used in photography.
Q183. What is the initial colour of ferrous sulphate crystals, and what is the colour of the residue after strong heating?
(1 mark)
Q184. Write the balanced chemical equation for the thermal decomposition of anhydrous ferrous sulphate.
(1 mark)
Q185. Give an example of a decomposition reaction caused by electricity.
(1 mark)
Q186. Why are decomposition reactions generally endothermic?
(1 mark)
Case Study 10 Context: Domestic electric circuits supply electricity through live, neutral, and earth wires. Appliances are connected in parallel to receive full voltage. Fuses or MCBs protect against overloading and short-circuiting.
Q187. Why are electrical appliances connected in parallel in a domestic circuit? Give one reason.
(1 mark)
Q188. What is the function of a fuse in a domestic circuit?
(1 mark)
Q189. What is overloading?
(1 mark)
Q190. What is the potential difference supplied to houses in India between the live and neutral wires?
(1 mark)
CLASS 10 CBSE SCIENCE
Final Section: The Expert Challenge (Q191–200)
This is the path-breaking section designed to test your ability to connect concepts, think critically, and apply science beyond the textbook. Completing this section will take your score to 100!
Q191. Design an experiment to prove that magnetic field lines around a solenoid resemble those of a bar magnet. Draw the diagram and explain.
(2 marks)
Q192. A student claims that respiration is both a biochemical and a physical process. Justify this statement with scientific reasoning.
(2 marks)
Q193. Compare the environmental impact of using detergents versus soaps. Suggest one eco-friendly alternative.
(2 marks)
Q194. Predict what would happen if sodium metal was accidentally dropped into water in a laboratory. Write the chemical equation and safety measures.
(2 marks)
Q195. Explain why tooth decay is considered a chemical process. Relate it to the concept of pH and acids.
(2 marks)
Q196. A CBSE examiner asks: “How does the law of conservation of mass apply to everyday cooking?” Give one example with a balanced equation.
(2 marks)
Q197. Imagine you are designing a new eco-friendly battery. Which metals or compounds would you choose, and why?
(2 marks)
Q198. A village has acidic soil with pH 4. Suggest a scientific plan to improve crop yield using chemistry concepts.
(2 marks)
Q199. Why is alternating current (AC) preferred over direct current (DC) for transmission? Explain with reference to transformers.
(2 marks)
Q200. Path-Breaker: “Science is not just about answers, but about asking better questions.” Write one original question that connects chemistry and physics, and explain why it matters.
(2 marks)