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Board Paper of Class 10 2015 Science (SET 3) - Solutions

(i) The questions paper comprises two section, A and B. You are to attempt both the sections.
(ii) All questions are compulsory.
(iii) There is no choice in any of the questions.
(iv) All questions of Section−A and all questions of Section−B are to be attempted separately.
(v) Question numbers 1 to 3 in Section−A are one mark questions. These are to be answered in one word or one sentence.
(vi) Question numbers 4 to 6 Section−A are two marks questions. These are to be answered in about 30 words each.
(vii) Question numbers 7 to 18 in Section−A are three marks questions. There are to be answered in about 50 words each.
(viii) Question numbers 19 to 24 in Section−A are five marks questions. These are to be answered in about 70 words each.
(ix) Question numbers 25 to 33 in Section−B are multiple choice questions based on practical skills. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you
(x) Question numbers 34 to 36 in Section B are two marks questions based on practical skills. These are to be answered in brief.

  • Question 1
    Write the name and molecular formula of the first member of the homologous series of alkynes. VIEW SOLUTION

  • Question 3
    List two examples of natural ecosystem. VIEW SOLUTION

  • Question 4
    Draw a labelled diagram to explain the formation of a rainbow in the sky. VIEW SOLUTION

  • Question 5
    Write two advantages of sustainable management of natural resources. Out of the two − reuse and recycle − which is better and why ? VIEW SOLUTION

  • Question 6
    List four advantages of conserving water in the form of ground water. VIEW SOLUTION

  • Question 7
    Write the name and structural formula of the compound formed when ethanol is heated at 443 K temperature with excess of conc. H2SO4. What is the role of conc. H2SO4 in this reaction? Also give the chemical equation for the reaction. VIEW SOLUTION

  • Question 8
    What is meant by functional group in carbon compounds? Write in tabular form the structural formula and the functional group present in the following compounds:
    (i) Ethanol
    (ii) Ethanoic acid VIEW SOLUTION

  • Question 9
    Four elements P, Q, R and S belong to the third period of the Modern Periodic Table and have, respectively 1, 3, 5 and 7 electrons in their outermost shells. Write the electronic configurations of Q and R and determine their valency. Write the molecular formula of the compound formed when P and S combine. VIEW SOLUTION

  • Question 10
    In the following table, the positions of six elements A, B, C, D, E and F are given as they are in the Modern Periodic Table :

    On the basis of the above table, answer the following questions :
    (i) Name the element which forms only covalent compounds.
    (ii) Name the element which is a metal with valency three.
    (iii) Name the element which is a non-metal with valency three.
    (iv) Out of B and C, whose atomic radius is bigger and why ?
    (v) Write the common name for the family to which the elements D and F belong. VIEW SOLUTION

  • Question 11
    Draw a diagram of the longitudinal section of a flower exhibiting germination of pollen on stigma and label (i) ovary, (ii) male germ-cell, (iii) female germ-cell and (iv) ovule on it. VIEW SOLUTION

  • Question 12
    Explain any three advantages of vegetative propagation. VIEW SOLUTION

  • Question 13
    What is placenta? Explain its function in humans. VIEW SOLUTION

  • Question 14
    "It is possible that a trait is inherited but may not be expressed." Give a suitable example to justify this statement. VIEW SOLUTION

  • Question 15
    "It is a matter of chance whether a couple will have a male or a female child." Justify this statement by drawing a flow chart. VIEW SOLUTION

  • Question 16

    A student wants to project the image of a candle flame on a screen 80 cm in front of a mirror by keeping the candle flame at a distance of 20 cm from its pole.

    (a) Which type of mirror should the student use?

    (b) Find the magnification of the image produced.

    (c) Find the distance between the object and its image.

    (d) Draw a ray diagram to show the image formation in this case and mark the distance between the object and its image.


  • Question 17
    What is meant by advance sunrise and delayed sunset? Draw a labelled diagram to explain these phenomena. VIEW SOLUTION

  • Question 18
    "Energy flow in food chains is always unidirectional". Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body. VIEW SOLUTION

  • Question 19
    What is speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Explain
    Define the terms 'nutrition' and 'nutrients'. List two differences between 'Holozoic nutrition' and 'Saprophytic nutrition'. Give two examples of each of these two types of nutrition.

  • Question 20
    (a) Identify A, B, C and D in the given diagram and write their names.

    (b) What is pollination ? Explain its significance.

    (c) Explain the process of fertilisation in flowers. Name the parts of the flower that develop after fertilisation into
    (i) seed,
    (ii) fruit. VIEW SOLUTION

  • Question 21
    What is meant by the power of a lens ? What is its S.I. unit ? Name the type of lens whose power is positive.
    The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens ? Draw ray diagram to justify your answer. VIEW SOLUTION

  • Question 22

    A student has focused the image of a candle flame on a white screen using a concave mirror. The situation is as given below :

    Length of the flame = 1.5 cm

    Focal length of the mirror = 12 cm

    Distance of flame from the mirror = 18 cm

    If the flame is perpendicular to the principal axis of the mirror, then calculate the following :

    (a) Distance of the image from the mirror

    (b) Length of the image

    If the distance between the mirror and the flame is reduced to 10 cm, then what would be observed on the screen? Draw ray diagram to justify your answer for this situation.


  • Question 23

    State the function of each of the following parts of the human eye:

    (i) Cornea

    (ii) Iris

    (iii) Pupil

    (iv) Retina

    Millions of people of the developing countries are suffering from corneal blindness. This disease can be cured by replacing the defective cornea with a cornea of a donated eye. Your school has organized a campaign in the school and its neighbourhood in order to create awareness about this fact and motivate people to donate their eyes after death. How can you along with your classmates contribute in this noble cause? State the objectives of organizing such campaigns in schools.


  • Question 24
    Elements forming ionic compounds attain noble gas electronic configuration by either gaining or losing electrons from their valence shells. Explain giving reason why carbon cannot attain such a configuration in this manner to form its compounds. Name the type of bonds formed in ionic compounds and in the compounds formed by carbon. Also explain the reason why carbon compounds are generally poor conductors of electricity.
    (1) ‘A’ is an element having four electrons in its outermost orbit. An allotrope ‘B’ of this element is used as a dry lubricant in machinery and in pencil leads. So
      (i) Write the name of element ‘A’ and its allotropes.
      (ii) State whether ‘B’ is a good conductor or non-conductor of electricity.
    (2) ‘E’ is an element which reacts with oxygen to form an oxide E2O. An aqueous solution of E2O turns red litmus blue, so
      (1) What is the nature of oxide E2O?
      (2) Write the name of element ‘E’.

  • Question 25
    A student obtained on a screen the sharp image of a candle flame placed at the farther end of laboratory table using a concave mirror. For getting better value of focal length of the mirror, the teacher suggested to him to focus the sun. What should the student do?

    (A) Should move the mirror away from the screen.
    (B) Should move the mirror towards the screen.
    (C) Should move the mirror and screen both towards the sun.
    (D) Should move only the screen towards the sun. VIEW SOLUTION

  • Question 26
    While determining the focal length of a convex lens, you try to focus the image of a distant object formed by the lens on the screen. The image formed on the screen, as compared to the object, should be
    (A) erect and highly diminished
    (B) erect and enlarged
    (C) inverted and enlarged
    (D) inverted and highly diminished VIEW SOLUTION

  • Question 27
    In which of the following four diagrams is the correct path of a ray of light passing through a glass prism shown ?


  • Question 28
    Which of the following is the best experimental set-up out of the four shown for tracing the path of a ray of light passing through a rectangular glass slab ?


  • Question 29
    A student takes 4 mL of distilled water in each of four test tubes I, II, III and IV, and then dissolves an equal amount of four different salts namely NaCl in I, CaCl2 in II, MgCl2 in III and KCl in IV. He then adds 8 drops of the given soap solution to each test tube and shakes the contents of the test tube 10 times. In which test tubes will enough lather (foam) be formed ?
    (A) I and II
    (B) II and III
    (C) I and IV

  • Question 30
    A student puts a drop of acetic acid first on a blue litmus paper and then on a red litmus paper. He would observe that VIEW SOLUTION

  • Question 31
    While studying saponification reactions, the following comments were noted down by the students :
    (I) Soap is a salt of fatty acids.
    (II) The reaction mixture is basic in nature.
    (III) In this reaction heat is absorbed.
    (IV) This reaction is not a neutralisation reaction.
    Which of these are the correct comments ?
    (A) I and III only
    (B) I, II and III
    (C) II, III and IV
    (D) I and II only VIEW SOLUTION

  • Question 32
    In a class, students were asked to observe the models/slides/pictures of the skeletons of forelimbs and wings of different organisms. After the observations the students made the following groups of homologous structures. Select the correct group :
    (A) Wings of a bird and a butterfly
    (B) Wings of a pigeon and a bat
    (C) Wings of a butterfly and a bat
    (D) Forelimbs of a cow, a duck and a lizard VIEW SOLUTION

  • Question 33
    A student is asked to study the different parts of an embryo of pea seeds. Given below are the essential steps for the experiment :
    (I) Soak the pea seeds in plain water and keep them overnight.
    (II) Cut open the soaked seed and observe its different parts.
    (III) Take some pea seeds in a petri dish.
    (IV) Drain the excess water. Cover the seeds with a wet cotton cloth and leave them as it is for a day.
    The correct sequence of these steps is
    (A) III, I, IV, II
    (B) III, IV, I, II
    (C) III, I, II, IV

  • Question 34
    A student places a 8.0 cm tall object perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. He obtains a sharp image of the object on a screen placed on the other side of the lens. What will be the nature (inverted, erect, magnified, diminished) of the image he obtains on a screen? Draw ray diagram to justify your answer. VIEW SOLUTION

  • Question 35
    A student is studying the properties of acetic acid. List two physical properties of acetic acid he observes. What happens when he adds a pinch of sodium hydrogen carbonate to this acid? Write any two observations. VIEW SOLUTION

  • Question 36
    A student is viewing under a microscope a permanent slide showing various stages of asexual reproduction by budding in yeast. Draw diagrams of what he sees (in proper sequence). VIEW SOLUTION
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