CBSE Class 10 Science Original Question Paper 2021
|Time: 3 Hours||Max Marks: 80|
- The question paper comprises five Sections A, B, C, D and E. You are to attempt All the sections.
- All questions are compulsory.
- Internal choice is given in Sections B, C, D and E.
- Questions number 1 and 2 in section A are one mark questions. They are to be answered in one word or in one sentence.
- Questions number 3 to 5 in Section B are two-marks questions. these are to be answered in about 30 words each.
- Questions number 6 to 15 in Section C are three-marks questions. These are to be answered in about 50 words each.
- Questions number 16 to 21 in Section D are five marks questions. These are to be answered in about 70 words each.
- Questions number 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.
- Write two advantages associated with water harvesting at the community level.
- Should the resistance of a voltmeter be low or high? Give reason.
- Draw electron dot structure of carbon dioxide and write the nature of bonding between and oxygen in its molecule.
List two properties of carbon which lead to the huge number of carbon compounds we see around us, giving reason for each.
- Give reason:
- Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
- Aluminium is a highly reactive metal; still, it is widely used in making cooking utensils.
- The power of a lens is +5 diopters. What are the nature and focal length of this lens? At what distance from this lens should an object be placed so as to get its inverted image of the same size?
- List two types of the transport system in human beings and write the functions of any one of these.
- Distinguish between pollination and fertilization. Mention the site and the product of fertilization in a flower.
- What is transpiration? List its two functions.
- What is translocation? Why is it essential for plants?
- Where do the substances in plants reach as a result of translocation?
- A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sum. He then directed the reflected light on to a sheet of paper held close to the mirror.
- What should he do burn the paper?
- Which type of mirror does he have?
- Will he be able to determine the approximate value of the focal length of this mirror from this activity? Give reason and draw ray diagram to justify your answer in this case.
A 10cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12cm. The distance of the object from the lens is 18cm. Find the nature, position and size of the image formed.
- List three environmental consequences of using fossil fuels. Suggest three steps to minimize the pollution caused by various energy sources.
- Write the essential function performed by ozone at the higher levels of the earths atmosphere? How is it produced? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. how can the use of these chemicals be reduced?
- (a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
- Dry hydrogen chloride gas dose not change the colour of dry litmus paper. Why?
How is sodium hydroxide manufactured in industries? Name the process. In this process a gas X is formed as by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reactions involved.
- On heating blue coloured powder of copper (II) nitrate in a boiling tube, black copper oxide, O2 and a brown gas X is formed.
- Identify the type of reaction and the gas X.
- Write balanced chemical equation of the reaction.
- Write the pH range of aqueous solution of the gas X.
- Which compounds are called (i) alkanes, (ii) alkenes and (iii) alkynes? C4H10 belongs to which of these? draw two structural isomers of this compound.
- What is amphoteric oxide? Give an example. Write balanced chemical equations to justify your answer.
16. (a) What are dominant and recessive traits?
(b)“It is possible that a trait is inherited but may not be expressed in the next generation?” Give a suitable example to justify this statement.
- (a) Why is the use of iodised salt advisable? Name the disease caused due to deficiency of iodine in our diet and state its one symptom.
(b) How do nerve impulses travel in the body? Explain.
What is hydrotropism? Design an experiment to demonstrate this phenomenon.
- (a) How will you infer with the help of an experiment that the same current flows through every part of a circuit containing three resistors in series connected to a battery?
(b) Consider the given circuit and find the current flowing in the circuit and potential difference across the 15 Ω resistors when the circuit is closed.
- Three resistors R1, R2, and R3 are connected in parallel and the combination is connected to a battery, ammeter, voltmeter and key. Draw suitable circuit diagram and obtain an expression for the equivalent resistance of the combination of the resistors.
- Calculate the equivalent resistance of the following network:
- Draw the pattern of magnetic field lines produced around a current carrying straight conductor passing perpendicularly through horizontal cardboard. State and apply right- hand thumb rule to make the direction of the field lines. How will the strength of the magnetic field change when the point where the magnetic field is to be determined is moved away from the straight conductor? Give a reason to justify your answer.
- (a) What is scattering of light? Explain how the colour of the scattered light depends on the size of the scattering particles.
- Explain the reddish appearance of the Sun at sunrise or sunset. Why dose it not appear red at noon?
- (a) List any three observations which posed a challenge to Mendeleev’s Periodic Law.
(b) How does the metallic character of elements vary on moving from-
- left to right in a period,
- from top to bottom in a group of the Modern Periodic Table?
Give reason for your answer.
The electrons in the atoms of four elements A, B, C and D are distributed in three shelled having 1,3,5 and 7 electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. Write the electronic configuration of the atoms of B and D and the molecular formula of the compound formed when B and D combined.
- List four precautions which a student should observe while preparing a temporary mount of a leaf peel to show stomata in his school laboratory.
- List in proper sequence four steps of obtaining germinating dicot seeds.
After examining a prepared slide under the high power of a compound microscope, a student concludes that the given slide shows the various stages of binary fission in a unicellular organism. Write two observations on the basis of which such a conclusion may be drawn.
- The current flowing through a resistor connected in a circuit and the potential difference developed across its ends are as shown in the diagram by millimeter and voltmeter readings respectively:
- What are the least counts of these meters?
- What is the resistance of the resistor?
- Draw the path of a ray of light when it enters one the faces of a glass slab at an angle of nearly 45o. Label on it (i) angle of refraction, (ii) angle of emergence and (iii) lateral displacement.
A student traces the path of a ray light through a glass prism as shown in the diagram, but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also label on it ∟i , ∟e, ∟r and ∟D.
- What is observed when a pinch of sodium hydrogen carbonate is added to 2ml of acetic acid taken in a test tube? Write chemical equation for the reaction involved in this case.
- A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct? Write its correct value stating the reason.
What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers?