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Board Paper of Class 10 2020 Science Delhi(Set 3) - Solutions

General Instructions:
Read the following instructions very carefully and strictly follow them:
(i) Question paper comprises three sections - A, B and C.
There are 30 questions in the question paper. All questions are compulsory.
(ii) Section A - question no. 1 to 14 - all questions or part thereof are of one mark each. These questions comprises multiple choice questions (MCQ), very short answer (VSA), and Assertion-Reason type questions. Answer to these questions should be given in one word or one sentence.
(iii) Section B - question no. 15 to 24 are short answer type questions, carrying 3 marks each. Answer to these questions should not exceed 50 to 60 words.
(iv) Section C - question no. 25 to 30 are long answer type questions, carrying 5 marks each. Answer to these questions should not exceed 80 to 90 words.
(v) Answer should be brief and to the point. Also the above mentioned word limit be adhered to as far as possible.
(vi) There is no overall choice in the question paper. However, an internal choice has been provided in some questions in each Section. Only one of the choices in such questions have to be attempted.
(vii) In addition to this, separate instructions are given with each section and question, wherever necessary.

  • Question 1
    Name a cyclic unsaturated carbon compound. VIEW SOLUTION

  • Question 2
    State an important advantage of using alternating current (a.c.) over direct current (d.c.). VIEW SOLUTION

  • Question 3
    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 for reproduction 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 is 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) What is the result of reckless female foeticide?
    (c) Which contraceptive method changes the hormonal balance of the body?
    (d) Write two factors that determine the size of a population. VIEW SOLUTION

  • Question 4
    Human body is made up of five important components, of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture.  Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradables, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

    (a) Why is the maximum concentration of pesticides found in human beings?
    (b) Give one method which could be applied to reduce our intake of pesticides through food to some extent.
    (c) Various steps in a food chain represent :

    (a) Food web
    (b) Trophic level
    (c) Ecosystem
    (d) Biomagnification

    (d) With regard to various food chains operating in an ecosystem, man is a:

    (a) Consumer
    (b) Producer
    (c) Producer and consumer
    (d) Producer and decomposer


  • Question 5
    Which one of the following is responsible for the sustenance of underground water?
    (a) Loss of vegetation cover
    (b) Diversion for high water demanding crops
    (c) Pollution from urban wastes
    (d) Afforestation VIEW SOLUTION

  • Question 6
    Incomplete combustion of coal and petroleum :
    (A) increases air pollution.
    (B) increases efficiency of machines.
    (C) reduces global warming.
    (D) produce poisonous gases.

    The correct option is:
    (a) (A) and (B)
    (b) (A) and (D)
    (c) (B) and (C)
    (d) (C) and (D) VIEW SOLUTION

  • Question 7
    When sodium hydrogen carbonate is added to ethanoic acid a gas evolves. Consider the following statements about the gas evolved?
    (A) It turns lime water milky.
    (B) It is evolved with a brisk effervescence.
    (C) It has a smell of burning sulphur.
    (D) It is also a by-product of respiration.
    The correct statements are:
    (a) (A) and (B) only
    (b) (B) and (D) only
    (c) (A), (C) and (D)
    (d) (A), (B) and (D) VIEW SOLUTION

  • Question 8
    When a small amount of acid is added to water, the phenomena which occur are:
    (A) Dilution
    (B) Neutralisation
    (C) Formation of H3O+ ions
    (D) Salt formation
    The correct statements are:
    (a) (A) and (C)
    (b) (B) and (D)
    (c) (A) and (B)
    (d) (C) and (D) VIEW SOLUTION

  • Question 9
    A real image is formed by the light rays after reflection or refraction when they:
    (A) actually meet or intersect with each other.
    (B) actually converge at a point
    (C) appear to meet when they are produced in the backward direction.
    (D) appear to diverge from a point.
    Which of the above statements are correct?
    (a) (A) and (D)
    (b) (B) and (D)
    (c) (A) and (B)
    (d) (B) and (C)


    Consider the following properties of virtual images:
    (A) cannot be projected on the screen
    (B) are formed by both concave and convex lens
    (C) are always erect
    (D) are always inverted
    The correct properties are:
    (a) (A) and (D)
    (b) (A) and (B)
    (c) (A), (B) and (C)
    (d) (A), (B) and (D) VIEW SOLUTION

  • Question 10
    At the time of short circuit, the electric current in the circuit :
    (a) vary continuously
    (b) does not change.
    (c) reduces substantially
    (d) increases heavily


    Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1A. The current through the 40W bulb will be:
    (a) 0.4 A
    (b) 0.6 A
    (c) 0.8 A

  • Question 11
    Calcium oxide reacts vigorously with water to produce slaked lime.
    CaO(s) + H2O(l) → Ca(OH)2(aq)
    This reaction can be classified as:
    (A) Combination reaction
    (B) Exothermic reaction
    (C) Endothermic reaction
    (D) Oxidation reaction
    Which of the following is a correct option?
    (a) (A) and (C)
    (b) (C) and (D)
    (c) (A), (C) and (D)
    (d) (A) and (B)


    When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:
    (a) Combination reaction
    (b) Displacement reaction
    (c) Decomposition reaction
    (d) Double displacement reaction VIEW SOLUTION

  • Question 12
    In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
    (A) exchange of atoms takes place
    (B) exchange of ions takes place
    (C) a precipitate is produced
    (D) an insoluble salt is produced
    The correct option is:
    (a) (B) and (D)
    (b) (A) and (C)
    (c) only (B)
    (d) (B), (C) and (D) VIEW SOLUTION

  • Question 13
    Two statements are given - one labelled  Assertion (A) and the other labelled Reason (R).
    Assertion (A): Esterification is a process in which a sweet smelling substance is produced.
    Reason (R) : When esters react with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.

    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. VIEW SOLUTION

  • Question 14
    Two statements are given - one labelled Assertion (A) and the other labelled Reason (R).

    Assertion (A) : A solar cooker cooks the meal due to green house effect.
    Reason (R) : The plane mirror is responsible for producing the green house effect.

    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 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. VIEW SOLUTION

  • Question 15
    (a) Write the mathematical expression for Joule's law of heating,
    (b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V. VIEW SOLUTION

  • Question 16
    Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead. VIEW SOLUTION

  • Question 17
    (a) Draw the structures for (i) ethanol, (ii) ethanoic acid.
    (b) Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction? Write the oxidising agent used in the reaction involved. VIEW SOLUTION

  • Question 18
    Name the parts (a) to (e) in the following diagram.

    What is the term given to the sequence of events occurring in the diagram?


    (a) What is tropism?
    (b) How do auxins promote the growth of a tendril around a support? VIEW SOLUTION

  • Question 19
    Why is Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect.


    Differentiate between a glass slab and a glass prism. What happens when a narrow beam of (i) a monochromatic light, and (ii) white light passes through (a) glass slab and (b) glass prism? VIEW SOLUTION

  • Question 20
    Define the term pollination. Differentiate between self pollination and cross pollination. What is the significance of pollination? VIEW SOLUTION

  • Question 21
    List the important products of the Chlor-alkali process. Write one important use of each.


    (a) How is washing soda prepared from sodium carbonate? Give its chemical equation.
    (b) State the type of this salt. Give one use of washing soda. VIEW SOLUTION

  • Question 22
    1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case. VIEW SOLUTION

  • Question 23
    The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye ? VIEW SOLUTION

  • Question 24
    What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer. VIEW SOLUTION

  • Question 25
    Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed :
    (i) between optical centre and principal focus of a convex lens.
    (ii) anywhere in front of a concave lens.
    (iii) at 2F of a convex lens.
    State the signs and values of magnifications in the above mentioned cases (i) and (ii).


    An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm.
    (i) At what distance from the mirror should a screen be placed in order to obtain a sharp image?
    (ii) Find the size of the image.
    (iii) Draw a ray diagram to show the formation of image in this case. VIEW SOLUTION

  • Question 26
    (a) What is the law of dominance of traits? Explain with an example.
    (b) Why are the traits acquired during the life-time-of-an individual not inherited? Explain. VIEW SOLUTION

  • Question 27
    (a) A gas is released during photosynthesis. Name the gas and also state the way by which the gas is evolved.
    (b) What are stomata? What governs the opening and closing of stomata?


    (a) Draw a diagram of human alimentary canal and label - gall bladder, pancreas, liver and small intestine on it.
    (b) Give two reasons to explain why absorption of digested food occurs mainly in the small intestine. VIEW SOLUTION

  • Question 28
    Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series ? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations. VIEW SOLUTION

  • Question 29
    The position of certain elements in the Modern Periodic Table are shown below.

    Using the above table answer the following questions giving reasons in each case :
    (1) Which element will form only covalent compounds?
    (ii) Which element is a non-metal with valency 2?
    (iii) Which element is a metal with valency 2?
    (iv) Out of H, C and F which has largest atomic size?
    (v) To which family does H, C and F belong?


    Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so? VIEW SOLUTION

  • Question 30
    (a) Explain with the help of the pattern of magnetic field lines the distribution of magnetic field due to a current carrying a circular loop.
    (b) Why is it that the magnetic field of a current carrying coil having n turns, is 'n' times as large as that produced by a single turn (loop)? VIEW SOLUTION
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