CBSE Class 10 Science Question Paper 2024 PDF (Set 1 - 31/2/1) is available for download here. CBSE conducted the Science exam on March 2, 2024, from 10:30 AM to 1:30 PM. The total marks for the theory paper are 80. The question paper contains 20% MCQ-based questions, 40% competency-based questions, and 40% short and long answer type questions.
CBSE Class 10 Science Question Paper 2024 (Set 1 - 31/2/1) with Answer Key
| CBSE Class 10 Science Question Paper 2024 (Set 1 - 31/2/1) with Answer Key |  Download |
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CBSE Science Question Paper (Set 1 – 31/2/1) 2024 Solution
| Question | Answer | Detailed Solution |
|---|---|---|
| 1. Solid Calcium oxide reacts vigorously with water to form Calcium hydroxide accompanied by the liberation of heat. From the information given above it may be concluded that this reaction: (A) is endothermic and pH of the solution formed is more than 7. (B) is exothermic and pH of the solution formed is 7. (C) is endothermic and pH of the solution formed is 7. (D) is exothermic and pH of the solution formed is more than 7. |
(D) is exothermic and pH of the solution formed is more than 7 | The reaction between calcium oxide (quicklime) and water is highly exothermic and produces calcium hydroxide (a strong base), which increases the solution’s pH: CaO (s) + H2O (l) → Ca(OH)2 (aq) + heat As calcium hydroxide is a base, the pH of the solution is greater than 7. |
| 2. Juice of tamarind turns blue litmus to red. It is because of the presence of an acid called: (A) methanoic acid (B) acetic acid (C) tartaric acid (D) oxalic acid |
(C) tartaric acid | Tamarind contains tartaric acid, a weak organic acid, which turns blue litmus red. This indicates the acidic nature of tamarind juice. |
| 3. Select from the following a process in which a combination reaction is involved: (A) Black and White photography (B) Burning of coal (C) Burning of methane (D) Digestion of food |
(B) Burning of coal | In burning of coal, carbon reacts with oxygen to form carbon dioxide, which is a combination reaction: C (s) + O2 (g) → CO2 (g) Two reactants combine to form a single product. |
| 4. The oxide which can react with HCl as well as KOH to give corresponding salt and water is: (A) CuO (B) Al2O3 (C) Na2O (D) K2O |
(B) Al2O3 | Al2O3 is an amphoteric oxide, which reacts with both acids and bases: Al2O3 + 6HCl → 2AlCl3 + 3H2O Al2O3 + 2KOH + 3H2O → 2K[Al(OH)4] This property makes it unique among the given options. |
| 5. Consider the following cases: (a) CaSO4 + Al (b) CuSO4 + Ca (c) FeSO4 + Cu (d) ZnSO4 + Mg The cases in which new products will form are: (A) (a) and (b) (B) (b) and (c) (C) (c) and (d) (D) (b) and (d) |
(D) (b) and (d) | Reactions occur only if the metal is more reactive than the one in the compound: (b) CuSO4 + Ca: Calcium displaces copper because calcium is more reactive. Ca + CuSO4 → CaSO4 + Cu (d) ZnSO4 + Mg: Magnesium displaces zinc because magnesium is more reactive. Mg + ZnSO4 → MgSO4 + Zn |
| 6. Identify the correct statement about the following reaction: 2H2S + SO2 → 2H2O + S (A) H2S is oxidising agent and SO2 is reducing agent. (B) H2S is reduced to sulphur. (C) SO2 is oxidising agent and H2S is reducing agent. (D) SO2 is oxidised to sulphur. |
(C) SO2 is oxidising agent and H2S is reducing agent | In this reaction: H2S is oxidized to sulphur, indicating that H2S acts as a reducing agent. SO2 is reduced to water, indicating that SO2 acts as an oxidizing agent. |
| 7. Consider the following statements about homologous series of carbon compounds: (a) All succeeding members differ by −CH2 unit. (b) Melting point and boiling point increases with increasing molecular mass. (c) The difference in molecular masses between two successive members is 16 u. (d) C2H2 and C2H4 are NOT the successive members of alkyne series. The correct statements are: (A) (a) and (b) (B) (b) and (c) (C) (a) and (c) (D) (c) and (d) |
(A) (a) and (b) | (a) Members of a homologous series differ by a CH2 unit. (b) Melting and boiling points increase with molecular mass. (c) Incorrect as the difference in molecular mass is 14 u. (d) Incorrect as C2H2 and C2H4 belong to different series. |
| 8. Which of the following statement(s) is (are) true about the human heart? (a) Right atrium receives oxygenated blood from lungs through pulmonary artery. (b) Left atrium transfers oxygenated blood to left ventricle which sends it to various parts of the body. (c) Right atrium receives deoxygenated blood through vena cava from upper and lower body. (d) Left atrium transfers oxygenated blood to aorta which sends it to different parts of the body. The correct statements are: (A) (a) (B) (a) and (d) (C) (b) and (c) (D) (b) and (d) |
(C) (b) and (c) | • (a) Incorrect as right atrium receives deoxygenated blood via vena cava. • (b) Correct as left atrium transfers oxygenated blood to left ventricle. • (c) Correct as right atrium receives deoxygenated blood from vena cava. • (d) Incorrect as left ventricle pumps blood into aorta. |
| 9. Select out of the following a gland which does NOT occur as a pair in the human body: (A) Pituitary (B) Ovary (C) Testis (D) Adrenal |
(A) Pituitary | The pituitary gland is a single gland located at the base of the brain. Other glands such as ovaries, testes, and adrenal glands occur as pairs in the human body. |
| 10. In human respiratory system, when a person breathes in, the position of ribs and diaphragm will be: (A) lifted ribs and curve/dome shaped diaphragm. (B) lifted ribs and flattened diaphragm. (C) relaxed ribs and flattened diaphragm. (D) relaxed ribs and curve/dome shaped diaphragm. |
(B) lifted ribs and flattened diaphragm | During inhalation: The ribs are lifted upward and outward, increasing chest cavity volume. The diaphragm contracts and flattens, creating a vacuum that draws air into the lungs. |
| 11. Identify the mode of asexual reproduction in the following organism: (A) Fragmentation (B) Multiple fission (C) Budding (D) Binary fission |
(C) Budding | Budding is a form of asexual reproduction where a new organism develops as an outgrowth or bud from the parent. Examples include Hydra and yeast. |
| 12. A cross made between two pea plants produces 50% tall and 50% short pea plants. The gene combination of the parental pea plants must be: (A) Tt and Tt (B) TT and Tt (C) Tt and tt (D) TT and tt |
(C) Tt and tt | The cross between Tt (heterozygous tall) and tt (homozygous short) produces: Tt (tall) : tt (short) = 1 : 1 50% of the offspring are tall, and 50% are short. |
| 13. Consider the following statements in the context of human eye: (a) The diameter of the eye ball is about 2.3 cm. (b) Iris is a dark muscular diaphragm that controls the size of the pupil. (c) Most of the refraction for the light rays entering the eye occurs at the crystalline lens. (d) While focusing on the objects at different distances the distance between the crystalline lens and the retina is adjusted by ciliary muscles. The correct statements are: (A) (a) and (b) (B) (a), (b) and (c) (C) (b), (c) and (d) (D) (a), (c) and (d) |
(A) (a) and (b) | (a) Correct: The diameter of the eyeball is approximately 2.3 cm. (b) Correct: The iris controls the size of the pupil. (c) Incorrect: Most refraction occurs at the cornea, not the lens. (d) Incorrect: The distance between the lens and retina is fixed; ciliary muscles adjust lens shape. |
| 14. The maximum resistance of a network of five identical resistors of 1/5 Ω each can be: (A) 1 Ω (B) 0.5 Ω (C) 0.25 Ω (D) 0.1 Ω |
(A) 1 Ω | To achieve maximum resistance, all resistors are connected in series: Rtotal = R1 + R2 + R3 + R4 + R5 Given each resistor has resistance of 1/5 Ω: Rtotal = 1/5 + 1/5 + 1/5 + 1/5 + 1/5 = 1 Ω |
| 15. Study the I-V graph for three resistors of resistances R1, R2, and R3 and select the correct statement: (A) R1 = R2 = R3 (B) R1 > R2 > R3 (C) R3 > R2 > R1 (D) R2 > R3 > R1 |
(C) R3 > R2 > R1 | The slope of the I-V graph represents resistance (R). A steeper slope indicates higher resistance: R3 has the steepest slope, so it has the highest resistance. R2 has a moderate slope, so it has intermediate resistance. R1 has the least steep slope, so it has the lowest resistance. |
| 16. Strength of magnetic field produced by a current-carrying solenoid DOES NOT depend upon: (A) number of turns in the solenoid (B) direction of the current flowing through it (C) radius of solenoid (D) material of core of the solenoid |
(B) direction of the current flowing through it | The strength of the magnetic field depends on: • The number of turns in the solenoid. • The material of the core. • The current flowing through the solenoid. However, the direction of the current affects the field's polarity, not its strength. |
| 17. Assertion (A): Different metals have different reactivities with water and dilute acids. Reason (R): Extraction of a metal from its ore depends on its position in the reactivity series. (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. |
(A) Both (A) and (R) are true and (R) is the correct explanation of (A) | The reactivity of metals varies, affecting their reactions with water and acids. The method of extraction (e.g., electrolysis for highly reactive metals) depends on their position in the reactivity series. |
| 18. Assertion (A): Human female has a perfect pair of sex chromosomes. Reason (R): Sex chromosome contributed by the human male in the zygote decides the sex of a child. (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. |
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A) | Human females have two identical sex chromosomes (XX). The sex of a child is determined by the sex chromosome (X or Y) contributed by the male, but this does not directly explain the "perfect pair" in females. |
| 19. Assertion (A): Myopic eye cannot see distant objects distinctly. Reason (R): For the correction of myopia, converging lenses of appropriate power are prescribed by eye-surgeons. (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. |
(C) (A) is true, but (R) is false | Myopia (near-sightedness) is corrected using diverging lenses, not converging lenses. The diverging lens helps focus distant objects on the retina, correcting the defect. |
| 20. Assertion (A): The deflection of a compass needle placed near a current-carrying wire decreases when the magnitude of an electric current in the wire is increased. Reason (R): Strength of the magnetic field at a point due to a current-carrying conductor increases on increasing the current in the conductor. (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. |
(D) (A) is false, but (R) is true | The deflection of a compass needle increases, not decreases, when the current in the wire increases. This is due to the increased strength of the magnetic field produced by the current-carrying conductor. |
| 21 (a)."No precipitation reaction can occur without exchange of ions between the two reactants." Justify this statement giving a balanced chemical equation for the reaction. | BaCl2 + Na2SO4 → BaSO4 + 2NaCl | A precipitation reaction occurs when two ionic solutions are mixed, and an insoluble compound (precipitate) is formed due to the exchange of ions: BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq) In this reaction, barium and sulfate ions combine to form insoluble BaSO4. |
| 21 (b). Giving one example of each, differentiate between a displacement reaction and a double displacement reaction. | Displacement: Zn + CuSO4 → ZnSO4 + Cu Double displacement: AgNO3 + NaCl → AgCl + NaNO3 |
Displacement Reaction: A more reactive element displaces a less reactive element from its compound. Example: Zn + CuSO4 → ZnSO4 + Cu Double Displacement Reaction: Two ionic compounds exchange their ions to form new compounds. Example: AgNO3 + NaCl → AgCl + NaNO3 |
| 22. Photosynthesis takes place in the leaves, and the food prepared by it reaches other parts of the plant. Name the process involved and explain it. | Translocation | Translocation is the movement of food (sucrose) from the leaves to other parts of the plant through phloem. This occurs by active transport using energy, driven by a pressure gradient in the phloem vessels. |
| 23. "Stability of DNA in a species is ensured during sexual reproduction." Justify the statement. | DNA stability is ensured by meiosis | During sexual reproduction, meiosis ensures that gametes have half the chromosome number. Fertilization restores the chromosome number, preserving DNA stability. Crossing over and recombination maintain genetic variation without altering the basic DNA structure. |
| 24 (a). State two laws of refraction of light. | 1. Incident ray, refracted ray, and normal lie in the same plane. 2. n = sin i / sin r |
1. The incident ray, refracted ray, and the normal to the surface at the point of incidence lie in the same plane. 2. The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is constant for a given pair of media: n = sin i / sin r |
| 24 (b). Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is 3 × 108 m/s. | v = 2 × 108 m/s | The absolute refractive index (n) of a medium is the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v): n = c / v Given n = 1.5 and c = 3 × 108 m/s: v = c / n = 3 × 108 / 1.5 = 2 × 108 m/s The speed of light in glass is 2 × 108 m/s. |
| 25 (a). Use Ohm’s law to determine the potential difference across the 3 Ω resistor in the circuit shown below when the key is closed: | V = 1 V | Total Resistance (Rtotal): All resistors (1 Ω, 2 Ω, 3 Ω) are in series: Rtotal = 1 + 2 + 3 = 6 Ω Current in the Circuit (I): Using Ohm’s law: I = V / Rtotal = 6 V / 6 Ω = 1 A Potential Difference Across the 3 Ω Resistor: V = I × R = 1 A × 3 Ω = 3 V |
| 26. Name the term used for the materials which cannot be broken down by biological processes. Give two ways by which they harm various components of an ecosystem. | Non-biodegradable materials | Non-biodegradable materials are substances that cannot be decomposed by natural biological processes. Harmful effects: 1. Soil and water pollution: These materials persist in the environment and contaminate natural resources. 2. Threat to wildlife: Animals ingest non-biodegradable materials, leading to injuries or poisoning. |
| 27. It is observed that Calcium on reaction with water floats on its surface. Explain why it happens. Write a balanced chemical equation for the reaction that occurs. What happens when the aqueous solution of the product of this reaction reacts with Carbon dioxide gas? Write a balanced chemical equation for the reaction. | Floating due to hydrogen gas bubbles | Calcium reacts with water to form calcium hydroxide and hydrogen gas. The hydrogen gas bubbles stick to the surface of calcium, making it float. Balanced chemical equation: Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g) When calcium hydroxide reacts with carbon dioxide, calcium carbonate is formed: Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l) |
| 28. Draw a labelled diagram to show electrolytic refining of copper. State what happens when electric current is passed through the electrolyte taken in this case. | Copper is refined; impurities settle as anode mud | Anode: Impure copper dissolves into the electrolyte. Cathode: Pure copper deposits on the cathode. Electrolyte: Acidified copper sulfate (CuSO4) solution. Impurities settle as anode mud, while pure copper is obtained at the cathode. |
| 29 (a). Give reasons for the following: (i) Alveoli in lungs are richly supplied with blood capillaries. (ii) Respiratory pigment in the blood takes up oxygen and not carbon dioxide. (iii) During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of CO2 in human beings. |
Efficient gas exchange; Hemoglobin affinity; Lactic acid formation | (i) Alveoli have a dense network of capillaries to ensure efficient gas exchange by maintaining a large surface area and proximity to the bloodstream. (ii) Hemoglobin, the respiratory pigment, has a higher affinity for oxygen than carbon dioxide, enabling effective oxygen transport. (iii) In humans, anaerobic respiration produces lactic acid (a 3-carbon molecule) due to insufficient oxygen, avoiding complete oxidation to CO2. |
| 29 (b). (i) Name the movements that occur all along the gut in the human digestive system. How do they help in digestion? (ii) Where is bile juice stored in the human body? List two roles of bile juice. |
Peristalsis; Gallbladder; Fat digestion and neutralization | (i) Movements: Peristalsis, which involves rhythmic contractions of the digestive tract, helps push food forward and mix it with digestive juices for effective digestion. (ii) Bile juice is stored in the gallbladder. Roles: 1. Emulsification of fats: Breaks down fat globules for easier digestion by enzymes. 2. Neutralization of stomach acid: Creates an alkaline environment suitable for enzymes in the small intestine. |
| 30 (a). Explain the events that take place once a sperm reaches the oviduct till it becomes a fetus. Write the role of placenta in pregnancy. | Fertilization, implantation, development; Placenta for nutrient exchange | Fertilization: Sperm fuses with an ovum in the oviduct to form a zygote. Implantation: The zygote undergoes cleavage to form an embryo, which implants in the uterine wall. Development: The embryo differentiates into specialized tissues and organs, eventually becoming a fetus. Role of Placenta: Facilitates nutrient, oxygen, and waste exchange between mother and fetus. Produces hormones like progesterone to support pregnancy. |
| 31. Define the term power of accommodation of the human eye. Write the name of the part of the eye which plays a major role in the process of accommodation and explain what happens when the human eye focuses on: (i) Nearby objects (ii) Distant objects |
Power of accommodation; Ciliary muscles; Lens adjustments | Power of accommodation: The ability of the human eye to adjust the focal length of its lens to focus on objects at varying distances. Part: Ciliary muscles. (i) Nearby objects: Ciliary muscles contract, making the lens thicker and increasing its refractive power. (ii) Distant objects: Ciliary muscles relax, making the lens thinner and reducing its refractive power. |
| 32. Draw a diagram to show the pattern of magnetic field lines on a horizontal sheet of paper due to a straight conductor passing through its center and carrying current vertically upwards. Mark on it: (i) The direction of current in the conductor. (ii) The corresponding magnetic field lines. State the right-hand thumb rule and check whether the directions marked by you are in accordance with this rule or not. |
Right-hand thumb rule verified | Right-hand thumb rule: If you hold a current-carrying conductor in your right hand with your thumb pointing in the direction of the current, the curl of your fingers shows the direction of magnetic field lines. The field lines around a straight conductor carrying current vertically upwards form concentric circles on the horizontal plane, with the direction following the right-hand thumb rule. |
| 33. Use of pesticides to protect our crops affects organisms at various trophic levels, especially human beings. Name the phenomenon involved and explain how it happens. | Biomagnification | Biomagnification refers to the increase in concentration of toxic substances like pesticides at successive trophic levels in a food chain. Pesticides persist in the environment and accumulate in small organisms like plankton. Larger organisms consume these smaller ones, leading to higher pesticide concentrations at each trophic level. Humans at the top of the food chain accumulate the highest levels, leading to health issues like nervous disorders and cancer. |
| 34 (a). (i) Give reason why carbon can neither form C4+ cations nor C4− anions but form covalent compounds. (ii) What is homologous series of carbon compounds? Write the molecular formula of any two consecutive members of homologous series of aldehydes. (iii) Draw the structure of the molecule of cyclohexane (C6H12). |
(i) Forms covalent bonds (ii) Methanal: HCHO; Ethanal: CH3CHO (iii) Cyclohexane structure provided |
(i) Carbon has four valence electrons. Losing or gaining four electrons requires a high amount of energy, making C4+ or C4− ions energetically unfavorable. Hence, it forms covalent bonds by sharing electrons. (ii) A homologous series is a group of compounds with the same functional group and general formula, where each successive member differs by a CH2 group. For aldehydes: Methanal (HCHO), Ethanal (CH3CHO). (iii) The structure of cyclohexane consists of six carbon atoms arranged in a ring, each bonded to two hydrogen atoms. |
| 34 (b). (i) Name a commercially important carbon compound having functional group −OH and write its molecular formula. (ii) Write chemical equations to show its reaction with: 1. Sodium metal 2. Excess concentrated sulfuric acid 3. Ethanoic acid in the presence of an acid catalyst 4. Acidified potassium dichromate. |
Ethanol (C2H5OH) Reactions as provided |
(i) Ethanol (C2H5OH) is a commercially important alcohol used as a solvent, in beverages, and as fuel. (ii) Reactions: 1. Reaction with sodium: C2H5OH + 2Na → 2C2H5ONa + H2 2. Reaction with concentrated sulfuric acid: C2H5OH → C2H4 + H2O (dehydration) 3. Reaction with ethanoic acid (esterification): C2H5OH + CH3COOH → CH3COOC2H5 + H2O 4. Reaction with acidified potassium dichromate (oxidation): C2H5OH → CH3COOH + H2O |
| 35 (a). (i) Distinguish between hormonal coordination in plants and animals. (ii) Which part of the brain is responsible for: 1. Intelligence 2. Riding a bicycle 3. Vomiting 4. Controlling hunger (iii) How is the brain and spinal cord protected against mechanical injuries? |
Hormonal distinction; Brain functions; Protection by cranium, meninges, CSF |
(i) Hormonal coordination: Plants: Use phytohormones (e.g., auxin) for slow, long-term responses. Animals: Use hormones secreted by endocrine glands for faster responses. (ii) Brain functions: 1. Intelligence: Cerebrum. 2. Riding a bicycle: Cerebellum. 3. Vomiting: Medulla oblongata. 4. Hunger control: Hypothalamus. (iii) Protection: Cranium and vertebral column provide structural protection. Meninges and cerebrospinal fluid (CSF) cushion against mechanical injuries. |
| 35 (b). (i) What are tropic movements? Give an example of a plant hormone which: 1. Inhibits growth 2. Promotes cell division (ii) Explain the directional movement of a tendril in a pea plant in response to touch. Name the hormone responsible for this movement. |
Tropic movements; Abscisic acid; Cytokinin; Auxin regulates tendril growth | (i) Tropic movements are directional growth responses in plants towards or away from external stimuli such as light, gravity, water, or touch. Hormone inhibiting growth: Abscisic acid (ABA) Hormone promoting cell division: Cytokinin (ii) Tendrils in pea plants show thigmotropism, a directional growth response to touch. When a tendril touches a support, the cells on the opposite side elongate more than the cells on the side of contact, causing the tendril to curl around the support. The hormone responsible for this movement is Auxin. |
| 36 (a). Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of the image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer. | Image at 2F on the other side; Real, inverted, same size | When the object is at 2F, the image forms at 2F on the other side, is real, inverted, and of the same size. If the upper half of the lens is covered, the entire image is formed but with reduced brightness. If uncovered, the image appears normal in brightness. Reason: The uncovered portion still refracts light to form the complete image. |
| 36 (b). An object is placed at a distance of 30 cm from the optical center of a concave lens of focal length 15 cm. Use the lens formula to determine the distance of the image from the optical center of the lens. Write the nature of the image formed. | v = −10 cm; Virtual, erect, diminished | Lens formula: 1/f = 1/v − 1/u Given: f = −15 cm (concave lens), u = −30 cm (object distance) Substituting values: 1/−15 = 1/v − 1/−30 Simplify: 1/−15 + 1/30 = 1/v LCM of 15 and 30 is 30: −2/30 + 1/30 = −1/30 v = −10 cm The image is formed at a distance of 10 cm on the same side as the object. Nature of the image: The image is virtual, erect, and diminished. |
| 37 (a). Salts play a very important role in our daily life. Sodium chloride, known as common salt, is used in almost every kitchen. Baking soda is another salt used in faster cooking and in the baking industry. (i) Identify the acid and base from which Sodium chloride is formed. (ii) Find the cation and the anion present in Calcium sulphate. (iii) Sodium chloride and washing soda both belong to the same family of salts. Justify this statement. |
Acid: HCl; Base: NaOH Cation: Ca2+; Anion: SO42− Belong to sodium salt family |
(i) Sodium chloride (NaCl) is formed from: Acid: Hydrochloric acid (HCl). Base: Sodium hydroxide (NaOH). (ii) Calcium sulphate (CaSO4) contains: Cation: Ca2+. Anion: SO42−. (iii) Sodium chloride and washing soda both contain sodium (Na+) ions, classifying them in the same family of salts derived from strong bases. |
| 37 (b). Find the cation and the anion present in Calcium sulphate. Sodium chloride and washing soda both belong to the same family of salts. Justify this statement. | Cation: Ca2+; Anion: SO42−; Sodium-based salts | Calcium sulphate (CaSO4) contains: Cation: Calcium ion (Ca2+). Anion: Sulfate ion (SO42−). Sodium chloride (NaCl) and washing soda (Na2CO3) both belong to the family of sodium salts because they share the same cation (Na+). Sodium chloride is formed from NaOH and HCl. Washing soda is formed from NaOH and H2CO3. Both are classified as salts of sodium hydroxide, making them part of the same family. |
| 38 (a). Which of the cut pieces of the two Planaria could regenerate to form a complete organism? | All cut pieces can regenerate | All cut pieces (L, M, N from Planaria A and O, P from Planaria B) are capable of regenerating into a complete organism. This is because Planaria has a high regenerative ability due to specialized stem cells called neoblasts, which enable the formation of missing body parts. |
| 38 (b). Give an example of another organism which follows the same mode of reproduction as Planaria. | Hydra | An example of another organism that follows regeneration is the Hydra. Like Planaria, Hydra can regenerate its entire body from small fragments due to its regenerative cells. |
| 38 (c). What is the meaning of ’development’ in regeneration? | Formation of missing or damaged parts | In regeneration, development refers to the process by which specialized cells (stem cells) proliferate, differentiate, and organize to form the missing or damaged parts of an organism. It involves: Proliferation: Growth and division of cells. Differentiation: Cells specialize to perform specific functions. Organization: Cells arrange themselves to restore the structure and functionality of the organism. |
| 38 (c) OR: Differentiate between regeneration and fragmentation. | Regeneration: Repair Fragmentation: Splitting into new individuals |
Regeneration: It refers to the process by which specialized cells repair or regrow missing parts of an organism (e.g., Planaria). It is primarily a repair mechanism but can result in new individuals in some cases. Fragmentation: It is a form of asexual reproduction where the body of an organism splits into two or more fragments, and each fragment grows into a new individual (e.g., Spirogyra). It is purely a mode of reproduction, unlike regeneration which is also involved in repair. |
| 39 (a). List two properties of heating elements. | High resistivity and high melting point | Properties of heating elements: 1.High resistivity: Ensures sufficient heat generation when current flows through the element. 2.High melting point: Prevents the element from melting under high temperatures. |
| 39 (b). List two properties of electric fuses. | Low melting point and specific current rating | Properties of electric fuses: 1. Low melting point: Ensures the fuse melts easily under excessive current to protect the circuit. 2. Specific current rating: Designed to allow a specific maximum current, preventing overheating of connected devices. |
| 39 (c). Name the principle on which an electric fuse works. Explain how a fuse wire is capable of saving electrical appliances from getting damaged due to accidentally produced high currents. | Heating effect of electric current | Principle: An electric fuse works on the heating effect of electric current. Explanation: When high current flows through the fuse wire, it generates heat due to its resistance. If the current exceeds the fuse’s rated capacity, the heat melts the fuse wire, breaking the circuit. This stops the flow of current, protecting electrical appliances from damage caused by excessive current. |
| 39 (c) OR: The power of an electric heater is 1100 W. If the potential difference between the two terminals of the heater is 220 V, find the current flowing in the circuit. What will happen to an electric fuse of rating 5 A connected in this circuit? | I = 5 A; Fuse may blow | To calculate current (I), use the formula: P = V × I Rearranging for I: I = P / V Given: P = 1100 W, V = 220 V I = 1100 / 220 = 5 A Since the current is equal to the fuse rating of 5 A, the fuse may blow if the current fluctuates or slightly exceeds the limit due to any surge in the circuit. |
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