2020 Class 10 Science Paper CBSE: Previous Year Questions with Answers

CBSE Class 10 Science 2020 Board Paper – Questions and Solutions

Class 10 Science Previous Year Question Paper 2020

Science [Set - 1]

Please check that this question paper contains 12 printed pages.

Code number given on the right hand side of the question paper should be written on the title page of the answer-book by the candidate.

Please check that this question paper contains 30 questions.

Please write down the Serial Number of the question before attempting it.

15 minute time has been allotted to read this question paper. The question paper will be distributed at 10.15 a.m. From 10.15 a.m. to 10.30 a.m., the students will read the question paper only and will not write any answer on the answer-book during this period.

Time allowed : 3 hours Maximum Marks : 80

SECTION – A

Q1. Name acyclic unsaturated carbon compound.

Answer: An acyclic unsaturated carbon compound is ethene (C₂H₄), which contains a carbon-carbon double bond and is not part of a ring structure.

Q2. The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.

Answer: The underlying phenomenon is electromagnetic induction.

Answer question numbers 3(a) to 3(d) and 4(a) to 4(d) on the basis of your understanding of the following paragraphs and the related studied concepts.

Q3. 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 the population.

(a) List two common signs of sexual maturation in boys and girls. 1 Mark

(b) What is the result of reckless female foeticide? [1M]

(d) Write two factors that determine the size of a population. [1M]

Answer: (a) In boys, common signs are growth of facial hair and deepening of voice. In girls, development of breasts and start of menstruation are seen.

(b) Reckless female foeticide leads to decrease in the number of females and results in an imbalanced sex ratio.

(d) The size of a population is determined by birth rate and death rate.

Q4. 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 biodegradable, 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? [1M]

(b) Give one method which could be applied to reduce our intake of pesticides through food to some extent. [1M]

(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 [1M]

Answer: (a) The maximum concentration of pesticides is found in humans due to biomagnification, as these non-biodegradable chemicals accumulate at each trophic level and humans are at the top.

(b) Washing fruits and vegetables properly before eating can reduce pesticide intake to some extent.

(d) Correct option: (a) Consumer

Q5. Calcium oxide reacts vigorously with water to produce slaked lime.

This reaction can be classified as:

(i) Combination reaction (ii) Exothermic reaction (iii) Endothermic reaction (iv) Oxidation reaction

Which of the following is a correct option ?

(a) (i) and (iii) (b) (iii) and (iv) (c) (i), (iii) and (iv) (d) (i) and (ii) [1M]

Answer: (d) (i) and (ii)

[ This reaction is a combination reaction because calcium oxide and water combine to form a single product, calcium hydroxide. It is also an exothermic reaction as a large amount of heat is released during the reaction.]

Q5. 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: [1M]

(a) Combination reaction (b) Displacement reaction (c) Decomposition reaction (d) Double displacement reaction

Answer: (d) Double displacement reaction

[ In this reaction, ions are exchanged between hydrogen sulphide and copper sulphate to form copper sulphide (black precipitate) and sulphuric acid, which is a characteristic of a double displacement reaction.]

Q6. In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution: [1M]

(i) exchange of atoms takes place

(ii) exchange of ions takes place

(iii) a precipitate is produced

(iv) an insoluble salt is produced

The correct option is:

(a) (ii) and (iv) (b) (i) and (iii) (c) only (ii) (d) (ii), (iii) and (iv)

Answer: (d) (ii), (iii) and (iv)

The reaction is:

(ii) exchange of ions takes place – The ions and combine, while and combine, so exchange of ions occurs.

(iii) a precipitate is produced – Barium sulphate () is an insoluble white precipitate.

(iv) an insoluble salt is produced – is an insoluble salt. ]

Q7. Baking soda is a mixture of: 1 Mark

(a) Sodium carbonate and acetic acid

(b) Sodium carbonate and tartaric acid

(d) Sodium hydrogen carbonate and acetic acid

Answer: (c) Sodium hydrogen carbonate and tartaric acid

[ Baking powder (commonly referred here) is a mixture of sodium hydrogen carbonate and tartaric acid, which helps in releasing carbon dioxide during baking.]

Q8.The chemical formula for plaster of Paris is: 1 Mark

(a) (b) (c) (d)

Answer: (c)

[ Plaster of Paris is calcium sulphate hemihydrates () , which contains half a molecule of water of crystallisation.]

Q9. The laws of reflection hold true for: 1 Mark

(a) plane mirrors only (b) concave mirrors only

Answer: (d) all reflecting surfaces

[The laws of reflection are valid for all types of reflecting surfaces, whether plane, concave or convex.]

Q9. When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is: [1M]

(a) real (b) inverted (c) virtual and inverted (d) virtual and erect

Answer: (d) virtual and erect

[ When an object is placed within the focal length of a concave mirror, the image formed is virtual, erect, and enlarged, and appears behind the mirror.]

10. At the time of short circuit, the electric current in the circuit: 1 Mark

(a) vary continuously (b) does not change (c) reduces substantially (d) increases heavily

10. 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: 1 Mark

(a) 0.4A (b) 0.6A (c) 0.8A (d) 1A

12. Incomplete combustion of coal and petroleum: 1 Mark

(i) increases air pollution.

(ii) increases the efficiency of machines.

(iii) reduces global warming.

(iv) produce poisonous gases.

The correct option is:

(a) (i) and (ii) (b) (i) and (iv) (c) (ii) and (iii) (d) (iii)and (iv)

For question numbers 13 and 14, two statements are given – one labeled Assertion (A) and the other labelled 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 correct explanation of the Assertion.

(b) Both A and R are true, but R is not the correct explanation of the Assertion.

(d) A is false but R is true.

13. 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. [1M]

14. Assertion (A): In the process of nuclear fission, the amount of nuclear energy generated by the fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

Reason (R): The nucleus of a heavy atom such as uranium, when bombarded with low energy neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the product nuclei gets converted to tremendous energy. [1M]

SECTION-B

15. 1g 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 reactions, the name and the color of the products formed in each case. [3M]

16. List the important products of the Chlor-alkali process. Write one important use of each. [3M]

16. How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it? [3M]

17. A 3 ml ethanol is taken in a test tube and warmed gently in a water bath. A 5% a solution of alkaline potassium permanganate is added first drop by drop to this solution, then in excess.

i) How is 5% solution of 4KMnO prepared?

(ii) State the role of alkaline potassium permanganate in this reaction. What happens when you add it in excess?

(iii) Write the chemical equation of this reaction. [3M]

18. A squirrel is in a scary situation. Its body has to prepare for either fighting or running away. State the immediate changes that take place in its body so that the squirrel is able to either fight or run? [3M]

18.Why is chemical communication better than electrical impulses as a means of communication between cells in a multicellular organism? [3M]

19. Define the term pollination. Differentiate between self pollination and cross pollination. What is the significance of pollination? [3M]

20. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor? Justify your answer. [3M]

21. Why is the Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect. [3M]

21. 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? [3M]

22. 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. [3M]

23. A V-I graph for a nichrome wire is given below. What do you infer from this graph? Draw a labelled circuit diagram to obtain such a graph. [3M]

24. (a) Write the mathematical expression for Joule’s law of heating: [3M]

(b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference 40 V.

SECTION-C

25. 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. [5M]

26. The position of certain elements in the Modern Periodic Table are shown below.

Group period	1	2	3 to 12	13	14	15	16	17	18
1	G								H
2	A			I			B		C
3		D			E				F

Using the above table answer the following questions giving reasons in each case:

(i) 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 the largest atomic size?

(v) To which family docs H, C and F belong? [5M]

26. 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? [5M]

27. (a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain. [5M]

(b) Draw a diagram of the human respiratory system and label - pharynx, trachea, lungs, diaphragm and alveolar sac on it.

27. (a) Name the organs that form the excretory system in human beings. [5M]

(b) Describe in brief how urine is produced in the human body.

28. (a) What is the law of dominance of traits? Explain with an example. [5M]

(b) Why are the traits acquired during the lifetime of an individual not inherited ? Explain.

29. Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed:

(i) between the optical centre and principal focus of a convex lens. State the signs and values of magnifications in the above-mentioned cases (i) and (ii). [5M]

(ii) anywhere in front of a concave lens.

(iii) at 2F of a convex lens.

29. An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm. [5M]

(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 the image in this case.

30. (a) What is an electromagnet? List any two uses. [5M]

(b) Draw a labelled diagram to show how an electromagnet is made.

(d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.