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CBSE Pre Board Class 10 2019 : Science (St Xavier's Sr. Sec. School, Delhi) : Set 2

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Pre Board Examination 2019 Std. 10 08-01-2019 Set 2 Max. Marks : 80 Time : 3 hrs. SCIENCE General Instructions: i) The question paper comprises of five sections A, B, C, D and E. You are to attempt all the sections. ii) All questions are compulsory. iii) Internal choice is given in sections B, C, D and E. iv) Question numbers 1 and 2 in Section-A are one mark questions. They are to be answered in one word or in one sentence. v) Question numbers 3 to 5 in Section- B are two marks questions. These are to be answered in about 30 words each. vi) Question numbers 6 to 15 in Section-C are three marks questions. These are to be answered in about 50 words each. vii) Question numbers 16 to 21 in Section-D are 5 marks questions. These are to be answered in about 70 words each. viii) Question numbers 22 to 27 in Section- E are based on practical skills. Each question is a two marks question. These are to be answered in brief. SECTION A 1. 2. In the following food chain, if 5 J of energy is available to man, how much energy will be available to plants? Plants sheep man 1 Name the green dot like structure in some cells observed by a student on a leaf slide. What is the green color due to? 1 SECTION B 3. A concave lens of focal length 15 cm forms an image at 10cm from the lens. a) Calculate the distance of the object from the lens b) What is the nature of image formed? (OR) The absolute refractive indices of two media A and B are 2.0 and 1.5 respectively. If the speed of light in medium B is 2x108 m/s. Calculate the speed of light in vacuum and in medium A. 2 4. Write balanced chemical equation for the following: a) Ca + H2O b) 5. MnO2 + Al 2 Answer the following questions: i) Colonies of yeast fail to multiply in water but multiply in sugar solution. Give one reason. ii) Where is the Zygote located in the flower after fertilization? 2 SECTION C 6. It is desired to obtain an erect image of an object using concave mirror of focal length of 12cm. a) What should be the range of distance of an object placed in front of the mirror? b) Will the image be smaller or bigger than the object? Give the related diagram. c) Where will be the image of this object formed if the object is now placed at 24cm from the mirror? Give the characteristics of the image formed in this case 3 7. Explain briefly: a) Ocean thermal energy b) Geothermal energy 8. 9. a) b) a) b) c) 3 Tap water conducts electricity where as distilled water does not. Why? What is meant by water of crystallization? Write the common name and chemical formula of a commercially important compound which has ten molecules of water of crystallization. 3 A green coating develops on the copper vessel in the rainy season. Why? A solution of substance X is used for white washing. i) Name the substance X and write its formula. ii) Write the reaction of the substance X named in (i) with water. 3 SCIENCE (Set 2) 10. a) b) 11. Page 2 Std. 10 In a village of Karnataka, people started cultivating crops all around a lake. They added fertilizer in the fields to increase the yield. Soon they discovered that water body was entirely covered with green floating plants and fish started dying in large numbers. Give reasons for excessive growth of plants and death of fishes in the lake. Although coal and petroleum are produced by degradation of bio mass, yet we need to conserve them. Why? 3 In a Guinea pig having black color 100 offsprings are produced. Out of which 75 were black and 25 were white. a) What is the possible genotype of hybrid pig? b) Which trait is dominant and which one is recessive? c) What is this cross called? What is the desired ratio of F1 generation? (OR) a) Draw neat and labeled diagram of Neuron and also explain the structure of it. b) Give one function for each of these hormones. i) Insulin ii) Thyroxine 3 12. State ohm s law. Write the necessary conditions for its validity. How is this law verified experimentally? What will be the nature of graph between the potential difference and current for the conductor? Name the physical quantity that can be obtained from this graph. 3 13. What are disadvantages of series circuit? Consider the following circuit diagram. If R1 = R2 = R3 = R4 = R5 = 3ohm, find the equivalent resistance of the circuit. (OR) What do you understand by series combination of resistors? Five resistors are connected in a circuit as shown. Find the ammeter reading when the circuit is closed. 14. a) b) c) a) b) 15. a) b) c) 3 State modern periodic law. What are the limitations of Newlands law of octave? Which element has twice as many electrons in its second shell as in its first shell? (OR) Give reason to explain why atomic radius increases on moving down in a group? From the following elements 4Be, 9F, 19K, 20Ca i) Select the two elements of the same group. ii) Explain which one is more metallic 19K or 20Ca? 3 What is the significance of emulsification of fats? Stomata of desert plants remains closed during day time. How do they take up carbon-di-oxide and perform photosynthesis? All plants give out oxygen during the day and CO2 during night. Do you agree with the statement? Give reasons. 3 SECTION D 16. a) b) A coil of insulated copper wire is connected to a galvanometer. What do you observe if a bar magnet is (i) pushed into the coil? (ii) held stationary inside the coil? Give the related diagram. (iii) withdrawn from inside the coil? What is a generator? On which principle is it based upon? What is the basic difference between AC and DC generator? Why is AC preferred over DC? 2+3 (OR) SCIENCE (Set 2) a) b) c) d) 17. a) b) c) 18. a) b) c) d) 19. a) b) c) d) a) b) c) d) 20. a) Std. 10 Draw a schematic diagram of a domestic circuit which has a provision of a main fuse, meter, one light bulb and a socket. Insulation cover of which colour is conventionally used for earth wire? Why is an earth wire connected to metallic parts of an appliance? Explain the term overloading of an electric circuit. Explain the role of fuse in an electric circuit. What is power of accommodation of human eye? Explain what happens to lens and ciliary muscles when a person sees nearby objects. Draw a ray diagram to show how farsightedness can be corrected using lens of appropriate focal length. What do you mean by recombination of the spectrum of white light? Write the reactions involved at cathode and anode during electrolytic reduction of molten NaCl. What do you mean by enrichment of ore? What are amphoteric oxides? Give example. State reason for the following: i) Ionic compounds have high melting and boiling point. ii) Hydrogen is not a metal but it has been assigned a place in the reactivity series of metals. 5 2+2+1 5 Give one advantage and one disadvantage of detergent over soap. Which of the following hydrocarbons undergo addition reaction: C2H6, C3H8, C3H6, C2H2, CH4 Write the molecular and structural formula of Pentanoic Acid. Write a chemical equation to represent the following reactions : i) Combustion of ethanol ii) Reaction between ethanoic acid and ethanol in presence of a drop of conc. H2SO4 (OR) Why does carbon form compounds mainly by covalent bonding? Draw the electron dot structure of ammonia molecule. At. No. N = 7, H = 1 Write the name and formula of the second member of homologus series having general formula CnH2n. An organic compound A of molecular formula C2H6O on heating with conc. Sulphuric acid gives compound B. Compound B on reduction in presence of Ni as a catalyst gives compound C. Name compounds A, B and C. Write chemical equation for the conversion of A into B. 5 b) Draw neat and labelled diagram of sectional view of heart and label the following: i) Largest artery ii) Upper chamber that receives oxygenated blood iii) Artery which carries deoxygenated blood iv) Largest vein that collects blood from lower part of body How does blood platelets save our lives during injury? 5 (OR) Draw neat and labeled diagram of human respiratory system and label the parts: i) That has cartilaginous rings ii) That encloses vocal cords iii) Dome shaped muscular partition that separates chest cavity from abdominal cavity iv) Main respiratory organ How are Alveoli designed to maximize the exchange of gases? a) b) c) d) What is placenta? Give its function. Explain one temporary and one permanent method of contraception. What harm is caused if testis in human males fail to descend into scrotal sacs? What changes are observed in the uterus if fertilization does not occur? b) a) 21. Page 3 (5) SCIENCE (Set 2) Page 4 Std. 10 SECTION E 22. In an experiment to study the relation between the potential difference across a resistor and the current through it, a student recorded the following observations: Potential difference (v) Current (A) 1.0 0.1 2.2 0.2 3.0 0.6 4.0 0.4 2 6.4 0.6 On examining the above observations, the teacher asked the student to reject one set of readings as the readings were incorrect. Which one of the above sets of readings can be rejected? Calculate the mean value of resistance of the resistor based on the remaining four sets of observations. 23. 24. In an experiment with a rectangular slab, a student observed that a ray of light incident at an angle of 55 with the normal on one face of a slab. After refraction, strikes the opposite face of the slab before emerging out into air making an angle of 40 with the normal. What value would you assign to the angle of refraction and angle of emergence? Draw a well labelled diagram also. (OR) Draw a labeled diagram to show refraction through a glass prism. For an equilateral prism, if angle of incidence is 35 and angle of emergence is 65 , what would be its angle of deviation? 2 Zinc granules were added to Zinc sulphate, Copper sulphate, Aluminium sulphate and Iron sulphate solutions taken in beaker no I, II, III, IV as shown in the figure given below: a) b) In which of the beakers, would you see the deposition of metal on Zinc? Why does the deposition not occur in other beakers? (OR) A student was provided with solutions of acetic acid, hydrochloric acid, sodium hydroxide and water. He was asked to report pH values using pH papers. He reported the pH values for the above solutions as 3, 1, 13 and 3 respectively. a) What was the mistake he committed? b) Which colour is given by pH paper with water and acetic acid? 2 25. List two observations which you make when a pinch of sodium hydrogen carbonate is added to acetic acid in a test tube. Write the chemical equation involved. 2 26. In the figure parts A and B are marked. Identify A and B and also write the conditions necessary for germinating seeds. OR What are cotyledons? How are number of cotyledons different in gram seed and maize (corn)? 2 27. What type of living organism is Yeast? Give its commercial importance? -x-x-x-x-x-x- 2

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