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CBSE Class 10 Pre Board 2021 : Science (R. B. K. School (RBK), Mira Road)

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PRELIMINARY EXAMINATION II (2020-21) SUBJECT: SCIENCE Grade: X Date :07/01/2021 Time: 3 hours Total Marks: 80 General Instructions: (i) The question paper comprises four sections A, B, C and D. There are 36 questions in the question paper. All questions are compulsory. (ii) Section A - question no. 1 to 20 - all questions and parts thereof are of one mark each. These questions contain multiple choice questions (MCQs), very short answer questions and assertion - reason type questions. Answers to these should be given in one word or one sentence. (iii) Section B - question no. 21 to 26 are short answer type questions, carrying 2 marks each. Answers to these questions should be in the range of 30 to 50 words. (iv) Section C - question no. 27 to 33 are short answer type questions, carrying 3 marks each. Answers to these questions should be in the range of 50 to 80 words. (v) Section D question no. - 34 to 36 are long answer type questions carrying 5 marks each. Answers to these questions should be in the range of 80 to 120 words. (vi) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions. (vii) Wherever necessary, neat and properly labeled diagrams should be drawn Section A QNo Mk 1) Why does silver chloride turn grey when exposed to sunlight? 1 2) Write the chemical name of the compound of sodium which is an ingredient in antacids. 1 3) What type of bond does carbon form with other elements? 1 4) Both a spherical mirror and a thin spherical lens have a focal length of (-15 cm). What type of mirror and lens are these? 1 5) A ray of light is incident at angle of 300 with the principal axis at the optical centre of the lens. What will be the angle of deviation. 1 6) A negatively charged particle is moving vertically upwards. When it enters a region of magnetic field directed towards the north, What is the direction of the force on the charge. 1 7) State the phenomenon involved in the blue color of sky. 1 8) Draw a diagram to represent uniform magnetic field in a given region. 1 9) As the object approaches the concave lens from infinity; the image moves from _______ to ________ 1 10) Name the causative agent of the disease kala-azar and its mode of asexual reproduction. 1 11) How does the acidic medium in the small intestine be converted into alkaline for pancreatic enzymes? 1 12) What do you mean by life processes? 1 13) What is the role of cartilaginous rings in trachea? 1 For question numbers 14, 15 and 16, two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below: a) Both A and R are true, and R is the correct explanation of the assertion. b) Both A and R are true, but R is not the correct explanation of the assertion. c) A is true, but R is false. d) A is false, but R is true. 14) Assertion(A) A geneticist crossed a pea plant having violet flowers with a pea plant of white flowers,he got all violet flowers in the first generation. Reason(R) White color gene is not passed on to the next generation. 1 15) Assertion (A) : Carbon has an extremely large number of compounds. Reason (R) : The chain of carbon atoms acts as backbone to which other atoms and functional group can be attached. 1 16) Assertion (A): A 200 W bulb glows with more brightness than 100 W bulb. Reason (R) : 100 W bulb has more resistance than 200 W bulb. 1 Q. No 17 - 20 contain five sub-parts each. You are expected to answer any four sub-parts in these questions. 17) Q17. Read the following passage and answer any four questions from 17(a) to 17(e). The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation production is gradual and takes place while general body growth is still going on some degree of sexual maturation does not necessarily mean that the mind or body ready for sexual acts or for having and bringing up children. Various contraceptive Devices are being used by human beings to control the size of population (a)List two common signs of sexual maturation in boys and girls (b)Reckless female foeticide results into declining child sex ratio call girls trafficking (i) declining child sex ratio (ii) girls trafficking (iii) difficulty in finding brides (iv) all of them (c) Which contraceptive method changes the hormonal balance of the body? (i)IUCDs (ii) Mechanical barriers (iii) Tubectomy (iv) Oral or vaginal pills (d) Two factors that determine the size of a population are (i) access to food and clean water (ii) rate of birth and rate of death (iii) poverty and education 4 (iv) employment and women empowerment (e) The success of birth control programmes in controlling population growth depends on (i) tubectomy (ii) use of contraceptive (iii) vasectomy (iv) acceptability of all above measures by people 18) Cops often use breathalysers to estimate the content of alcohol in a rider's breath. Do you know the breath analyser employs the chemical principle of redox reactions? Once a rider breathes into a breathalyzer, an acid solution of potassium dichromate reacts with it. The ethanol in the breath is oxidized to acetic acid; where the chromium (IV) in the Orange Yellow dichromate iron is reduced to chromium (III) which is green in colour. The amount of colour change Corresponds to levels of alcohol in the blood. a) Redox reaction is one in which i) oxidation takes place iii) both take place simultaneously 4 ii) reduction takes place iv) none of above b) Which substance gets oxidised when the food becomes rancid? i) oil in the food ii) spices in the food iii) salt in the food iv) all the ingredients c) What is the role of potassium dichromate in its reaction with ethanol to produce acetic acid? i) oxidising agent ii) reducing agent iii) catalyst iv) moderator d) The loss of oxygen or addition of hydrogen in a substance is called i) Reduction ii) oxidation iii) reduction oxidation iv) all of them 19) Fleming's Left-Hand Rule is a simple and accurate way to find the direction of force/motion of the conductor in an electric motor when the magnetic field direction and the current direction are known. This is the same law that governs the working of an electric motor, for that case, any electrical appliance or gadget; that exhibits any type of motion. a) When is the force experienced by the conductor maximum? b) State the principle of an electric motor. 4 c) A beam of electrons entering the region between two magnetic plates P1 and P2 experiences an upward force. Determine the North and South poles from the P1 and P2. d) Why do we use coils instead of single wire in motors? e) What is the function of split rings in a motor? 20) There are three main phenomena learnt in the chapter Human Eye and Colorful World viz. Atmospheric Refraction, Dispersion, Scattering. a) State two effects caused by atmospheric refraction b) Danger signals are always in red. State the phenomenon involved. c) What are the phenomena involved in formation of rainbows other than refraction? d) In dispersion, the color that undergoes maximum deviation is __________________ e) How does atmospheric refraction alter the position of star seen from earth? 4 Section B 21) What is lymph? Write its important functions. 2 22) a.Give reason why multicellular organisms require special organs for exchange of gases between their body and their environment. 2 b.Why do aquatic animals breathe faster than the terrestrial animals 23) Give two structural isomers for pentane. 2 24) Name the following: a) A metal, which is preserved in kerosene. b) A lustrous coloured non-metal. c) A metal, which can melt while kept on the palm. d) A metal, which is a poor conductor of heat. 2 25) Why do stars appear to twinkle? 2 26) Four resistors of 2 ohm each are joined end to end to form a square ABCD. Calculate the equivalent resistance of the combination between any two adjacent corners. 2 Section C 27) Write full form of AIDS.What is its causative agent?How does it spread and how can it be prevented? 3 28) Explain with the help of a diagram where and how urine is produced? 3 29) Plastic cups were used to serve tea in trains in early days; these could be returned to the vendors,cleaned and reused. Later kullads were used instead of plastic cups. Now paper cups are used for serving tea.What are the reasons for the shift from Plastic to Kulhads and then finally to paper cups? 3 30) Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and C. 3 31) The electronic configuration of an element X is 2,8,8,2. To which a) period and group of the modern periodic table does X belong? State its valency. Justify your answer in each case. 3 32) 33) a) In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode? b) What is observed when a solution of potassium iodide is added to a solution of Lead Nitrate in a test tube? What type of reaction is this? Explain with diagram, advanced sunrise. 3 3 Section D 34) Of the three metals X, Y and Z. X reacts with cold water. Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity 5 35) a) What is pollination? b) Differentiate between cross pollination and self pollination. c) How does pollination lead to fertilization?Explain with a labelled diagram. 5 36) a) 3 resistors R1, R2, R3 are connected in series to a battery V. Draw the circuit diagram showing the arrangement. Derive an expression for the equivalent resistance of the combination. b) If R1 = 10 , R2 = 20 and R3 = 30. calculate the effective resistance when they are connected in series. Also calculate the current flowing when the combination is connected to a 6V battery. 5 =================xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx===========

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