# CBSE Class 10 Science Question Papers 2020

CBSE Class 10 Science exam was conducted on 4th March 2020. The paper was of 80 marks consisting of 3 hours of time duration. Students found the Science paper is of moderate difficulty level. Here we are providing the CBSE Class 10 Science Question Papers 2020 consisting of all 3 sets. Going through these sets of papers will give students an idea of what kind of questions are asked in the Class 10 Science exam.

## CBSE Class 10 Science Question Paper 2020 – All Sets

Click on the link below to access the CBSE Class 10 Science Question Papers 2020 for all types of sets.

CBSE Class 10 Science Question Paper 2020 Set 1

CBSE Class 10 Science Question Paper 2020 Set 2

CBSE Class 10 Science Question Paper 2020 Set 3

## CBSE Class 10 Science Question Paper 2020 Set 1

Students can have a look at the CBSE Class 10 Science Question Paper 2020 Set 1 below:

### Science Set 1 Question Paper 2020

General Instructions:

I. This question paper comprises four sections – A, B and C. There are 30 questions in the question paper. All questions are compulsory.

II. Section A: Question numbers 1 to 14 – all questions or part thereof are of one marl each.These questions comprise multiple choice questions(MCQ), Very Short answer (VSA)and Assertion-Reason type question.Answer to these questions should be given in one word or one sentence.

III. Section B: Question numbers 15 to 24 are short answer type questions, carrying 3 marks each. Answers to these questions should not exceed 50 to 60 words.

IV. Section C: Question numbers 25 to 30 are long answer type questions, carrying 5 marks each. Answer to these questions should not exceed 80 to 90 words

V. Answers 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.

#### SECTION – A [14 × 1 = 14 MARK]

1. Write the number of valence electrons present in nitrogen atom $\left( _{7}^{14}N \right)$

2. Define the term induced electric current.

3. Answer question numbers 3(a) – 3(d) on the basis of your understanding of the following paragraph and the related concepts.

Around the year 1800, only 30 elements were known Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Mendeleev for classifying elements goes to Mendeleev for his most important contribution to the early development of a periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The format of their hydrides and oxides were treated as basic criteria for the classification of the elements. However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.

3(a). State Mendeleev’s periodic law.

3(b). Why did Mendeleev leave some gaps in the periodic table?

3(c). If the letter ‘R’ was used to represent and of the elements in the group, then the hydride and oxide of carbon would respectively be represented as

(i) $RH_{4}$, RO

(ii) $RH_{4}$, $RO_{2}$

(iii) $RH_{2}$, $RO_{2}$

(iv) $RH_{2}$, RO

3(d). Isotopes are

(i) Atoms of elements with similar chemical properties but different atomic masses.

(ii) Atoms of different elements with similar chemical properties but different atomic masses.

(iii) Atoms of elements with different chemical properties but same atomic masses.

(iv) Atoms of different elements with different chemical properties but same atomic masses.

4. Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts:

India today is facing the problem of overuse of resources, contamination of water and soil and luck of methods of processing the waste. The time has come for the world to say goodbye to “single-use plastics”. Steps must be undertaken to develop environment -friendly substitutes, effective plastic waste collection and methods of its disposal.

Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques. Bioremediation involves introducing microbes into a landfill to naturally ‘break’ it down and biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component. The city managed to chip away 15 lakh metric tonnes of waste at a cost of around Rs 10 crore. A similar experiment was successfully carried out in Ahmedabad also.

4(a). State two methods of effective plastic waste collection in your school.

4(b). Name any two uses of “single-use plastic” in daily life.

4(c). If we discontinue the use of plastic, how can an environment-friendly substitute be provided?

4(d). Do you think microbes will work similarly in landfill sites as they work in the laboratory? Justify your answer.

5. Which one of the following statements is correct about the human circulatory system?

I. Blood transports only oxygen and not carbon dioxide.

II. Human heart has five chambers

III. Valves ensure that the blood does not flow backwards.

IV. Both oxygen-rich and oxygen-deficient blood gets mixed in the heart.

6. Anaerobic process

I. Takes place in yeast during fermentation

II. Takes place in the presence of oxygen

III. Produces only energy in the muscles of human beings.

IV. Produces ethanol, oxygen and energy

(OR)

Most of the digestion and absorption of the food takes place in the

I. Small intestine

II. Liver

III. Stomach

IV. Large intestine

7. Fertilization is the process of

I. Transfer of male gamete to female gamete

II. Fusion of nuclei of male and female gamete.

III. Adhesion of ale and female reproductive organs

IV. The formation of gametes by a reproductive organ

8. If a person has five resistors each of value 1/5 Ω, then the maximum resistance he can obtain by connecting them is

a) 1 Ω

b) 5 Ω

c) 10 Ω

d) 25 Ω

(OR)

The resistance of a resistor is reduced to half of its initial value. In doing so, if other parameters of the circuit remain unchanged, the heating effects in the resistor will become

a) Two times

b) Half

c) One-fourth

d) Four times

9. Fleming’s Right-hand rule gives

a) Magnitude of the induced current

b) Magnitude of the magnetic field

c) Direction of the induced current

d) Both, direction and magnitude of the induced current

10. Which one of the following statements is not true about nuclear energy generation in a nuclear reactor?

a) Energy is obtained by a process called nuclear fission.

b) The nucleus of Uranium is bombarded with high energy neutrons.

c) A chain reaction is set in the process.

d) In this process a tremendous amount of energy is released at a controlled rate.

(OR)

The biggest source of energy on Earth’s surface is

a) Biomass

c) Tides

d) Winds

11. Food web is constituted by

I. Relationship between the organisms and the environment

II. Relationship between plants and animals

III. Various interlinked food chains in an ecosystem

IV. Relationship between animals and environment

12. Choose the incorrect statement from the following :

I. Ozone is a molecule formed by three atoms of oxygen

II. Ozone shields the surface of the Earth from ultraviolet radiations

IV. Ozone gets decomposed by UV radiations

For question numbers 13 and 14, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

1. Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

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

3. (A) is true, but (R) is false. (d) (A) is false, but (R) is true.

13. Assertion & Reasoning Questions:

Assertion (A): Following is a balanced chemical equation for the action of steam iron:

$3Fe + 4H_{2}O\rightarrow Fe_{3}O_{4} + 4H_{2}$

Reason (R): The law of conservation of mass holds good for a chemical equation.

14. Assertion (A): The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father.

Reason (R): A child who inherits X’ chromosome from his father would be a girl (XX), while a child who inherits a Y’ chromosome from the father would be a boy (XY).

#### SECTION – B [10 × 3 = 30 MARKS]

15. Lead Nitrate solution is added to a test tube containing potassium iodide solution.

(a) Write the name and colour of the compound precipitated.

(b) Write the balanced chemical equation for the reaction involved.

(OR)

What happens when food materials containing fats and oils are left for a long time?

List two observable changes and suggest three ways by which this phenomenon can be prevented.

16. List three differentiating features between the process of galvanization and alloying.

(OR)

Compare in tabular form the reactivity of the following metals with cold and hot water.

a) Sodium

b) Calcium

c) Magnesium

17. Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group?

18. A cheetah, on seeing a prey, moves towards him at a very high speed. What causes the movement of his muscles? How does the chemistry of cellular components of muscles change during this event?

19. Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.

20. Define the term evolution. “Evolution cannot be equated with progress.” Justify this statement.

(OR)

“During the course of evolution, organs or features may be adapted for new functions.” Explain this fact by choosing an appropriate example.

21. A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm ?
(a) Position of the image
(b) Size of the image
(c) Nature of the image
Draw a labelled ray diagram to justify your inferences.

22. The refractive index of a medium x’ with respect to a medium y’ is 2/3 and the refractive index of medium y’ with respect to medium z’ is 4/3. Find the refractive index of medium z’ with respect to medium x’. If the speed of light in medium x’ is 3 x 108 ms-1, calculate the speed of light in medium ‘y’.

23. A person may suffer from both myopia and hypermetropia defects.
(a) What is this condition called?
(b) When does it happen?
(c) Name the type of lens often required by the persons suffering from this defect.
Draw labelled diagrams of such lenses.

24. How will you use two identical glass prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw and label the ray diagram.

#### SECTION – C [6 × 5 = 30 MARKS]

25. A cloth strip dipped in onion juice is used for testing a liquid “x”. The liquid “x” changes its colour. Which type of an indicator is onion juice.

The juice “x” turns blue litmus red. List observations the liquid “x” will show on reacting with the following.

a) Zinc granules

b) Solid sodium carbonate

Write the chemical equations for the reactions involved.

(OR)

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

26. a) i) Write two properties of gold which make it the suitable metal for ornaments.

ii) Name two metals which are the best conductors of heat.

iii) Name two metals which melt when you keep them on your palm.

b) Explain the formation of ionic compound CaO with electron – dot structure.

Atomic numbers of calcium & oxygen are 20 & 8 respectively.

27. Why is nutrition necessary for the human body?

(b) What causes movement of food inside the alimentary canal?

(c) Why is the small intestine in herbivores longer than in carnivores?

(d) What will happen if mucus is not secreted by the gastric glands?

28. Draw a neat diagram showing fertilisation in a flower and label

(a) Pollen tube,

(b) Male germ cell and

(c) Female germ cell, on it.

Explain the process of fertilisation in a flower. What happens to the (i) ovary and (ii) ovule after fertilisation?

(OR)

(a) What is puberty?

(b) Describe in brief the functions of the following parts in the human male reproductive system:

(i) Testes

(ii) Seminal vesicle

(iii) Vas deferens

(iv) Urethra

(c) Why are testes located outside the abdominal cavity ?

(d) State how sperms move towards the female germ cell.

29. Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of 10 Ω, 20 Ω and 30 Ω connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following :

(a) Current through each resistor

(b) Total current in the circuit

(c) Total effective resistance of the circuit

(OR)

Two identical resistors, each of resistance 15 Ω, are connected in (i) series, and (ii) parallel, in turn to a battery of 6 V. Calculate the ratio of the power consumed in the combination of resistors in each case

30. (a) State Fleming’s Left-hand rule.

(b) List three characteristic features of the electric current used in our homes.

(c) What is a fuse? Why is it called a safety device?

(d) Why is it necessary to earth metallic electric appliances?

## CBSE Class 10 Science Question Paper 2020 Set 2

Students can have a look at the CBSE Class 10 Science Question Paper 2020 Set 2 below:

### Science Set 2 Question Paper 2020

General Instructions:

I. This question paper comprises four sections – A, B and C. There are 30 questions in the question paper. All questions are compulsory.

II. Section A: Question numbers 1 to 14 – all questions or part thereof are of one marl each.These questions comprise multiple choice questions(MCQ), Very Short answer(VSA)and Assertion-Reason type question.Answer to these questions should be given in one word or one sentence.

III. Section B: Question numbers 15 to 24 are short answer type questions, carrying 3 marks each. Answers to these questions should not exceed 50 to 60 words.

IV. Section C: Question numbers 25 to 30 are long answer type questions, carrying 5 marks each.Answer to these questions should not exceed 80 to 90 words

V. Answers 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.

#### SECTION – A [14 × 1 = 14 MARKS]

1. Which oil should be chaser for cooking to remain healthy?

2. Define the term induced electric current.

3. Answer question numbers 3(a) – 3(d) on the basis of your understanding of the following paragraph and the related concepts.

Around the year 1800, only 30 elements were known Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Mendeleev for classifying elements goes to Mendeleev for his most important contribution to the early development of a periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The format of their hydrides and oxides were treated as basic criteria for the classification of the elements. However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.

3(a). State Mendeleev’s periodic law.

3(b). Why did Mendeleev leave some gaps in the periodic table?

3(c). If the letter ‘R’ was used to represent and of the elements in the group, then the hydride and oxide of carbon would respectively be represented as

(i) $RH_{4}$, RO

(ii) $RH_{4}$, $RO_{2}$

(iii) $RH_{2}$, $RO_{2}$

(iv) $RH_{2}$, RO

3(d). Isotopes are

(i) Atoms of elements with similar chemical properties but different atomic masses.

(ii) Atoms of different elements with similar chemical properties but different atomic masses.

(iii) Atoms of elements with different chemical properties but same atomic masses.

(iv) Atoms of different elements with different chemical properties but same atomic masses.

4. Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts:

India today is facing the problem of overuse of resources, contamination of water and soil and luck of methods of processing the waste. The time has come for the world to say goodbye to “single-use plastics”. Steps must be undertaken to develop environment -friendly substitutes, effective plastic waste collection and methods of its disposal.

Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques. Bioremediation involves introducing microbes into a landfill to naturally ‘break’ it down and biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component. The city managed to chip away 15 lakh metric tonnes of waste at a cost of around Rs 10 crore. A similar experiment was successfully carried out in Ahmedabad also.

4(a). State two methods of effective plastic waste collection in your school.

4(b). Name any two uses of “single-use plastic” in daily life.

4(c). If we discontinue the use of plastic, how can an environment-friendly substitute be provided?

4(d). Do you think microbes will work similarly in landfill sites as they work in the laboratory? Justify your answer.

5. Fertilization is the process of

I. Transfer of male gamete to female gamete

II. Fusion of nuclei of male and female gamete.

III. Adhesion of male and female reproductive organs

IV. The formation of gametes by a reproductive organ

6. In the excretory system of human beings, some substances in the initial filtrate such as glucose, amino acids, salts and water are selectively reabsorbed in

(a) Urethra

(b) Nephron

(c) Ureter

(OR)

Pseudopodia are

(a) Small hair-like structures present on unicellular organisms

(b) False feet developed in some unicellular organisms

(c) Long, tube-like structures coming out of the mouth

(d) Suckers which are attached to the walls of the intestines

7. Which one of the following statements is correct about the human circulatory system?

I. Blood transports only oxygen and not carbon dioxide

II. Human heart has five chambers

III. Valves ensure that the blood does not flow backwards

IV. Both oxygen-rich and oxygen-deficient blood gets mixed in the heart

8. Which one of the following statements is not true about nuclear energy generation in a nuclear reactor?

(a) Energy is obtained by a process called nuclear fission.

(b) The nucleus of Uranium is bombarded with high energy neutrons.

(c) A chain reaction is set in the process.

(d) In this process a tremendous amount of energy is released at a controlled rate.

(OR)

The biggest source of energy on Earth’s surface is

(a) Biomass

(c) Tides

(d) Winds

9. If a person has five resistors each of value 1/5 Ω, then the maximum resistance he can obtain by connecting them is

(a) 1 Ω

b) 5 Ω

c) 10 Ω

d) 25 Ω

(OR)

The resistance of a resistor is reduced to half of its initial value. In doing so, if other parameters of the circuit remain unchanged, the heating effects in the resistor will become

I. Two times

II. Half

III. One-fourth

IV. Four times

10. Fleming’s Right-hand rule gives

I. Magnitude of the induced current

II. Magnitude of the magnetic field

III. Direction of the induced current

IV. Both, direction and magnitude of the induced current

11. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

a) 100 %

b) 10 %

c) 1 %

d) 0.1 %

12. Choose the incorrect statement from the following :

I. Ozone is a molecule formed by three atoms of oxygen

II. Ozone shields the surface of the Earth from ultraviolet radiations

IV. Ozone gets decomposed by UV radiations

For question numbers 13 and 14, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(1) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

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

(3) (A) is true, but (R) is false. (d) (A) is false, but (R) is true

13. Assertions (A): The reaction is MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 an example of a redox reaction.

Reason (R): In this reaction, HCL is reduced to Cl2 whereas MnO2 is oxidized to MnCl2.

14. Assertion (A): Wring of an insect and wing of a bird are analogous organs.

Reason (R): The organs which are quite different in fundamental structure and origin but perform the same function in different species are called analogous organs.

#### SECTION – B [10 × 3 = 30 MARKS]

15. When hydrogen sulphide gas is passed through a blue solution of copper sulphate, the colour of the solution fades and a black precipitation is obtained.

(a) Name the type of reaction mentioned above.

(b) Why does the colour of the solution disappear?

(c) Write the chemical name of the black precipitate formed.

(d) Give the balanced chemical equation for the reaction involved.

(OR)

Study the figure given below and answer the following questions.

I. Name the process depicted in the diagram.

II. Write the composition of the anode and the cathode.

III. Write the balanced chemical equation of the reaction taking place in this case.

IV. The reaction does not take place if a few drops of dilute sulphuric acid are not added to water. Why?

16. A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm?

(a) Position of the image

(b) Size of the image

(c) Nature of the image

Draw a labelled ray diagram to justify your inferences.

17. Define the term evolution. “Evolution cannot be equated with progress”. Justify this statement.

(OR)

“During the course of evolution, organs or features may be adapted for new functions. “ Explain this fact by choosing an appropriate example.

18. Write in tabular form the location and function of the hormones secreted by each of the following glands present in the human body.

19. List three differentiating features between the process of galvanization and alloying.

(OR)

Compare in tabular form the reactivity of the following metals with cold and hot water.

a) Sodium

b) Calcium

c) Magnesium

20. Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group? Explain.

21. Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.

22. (a) For the same angle of incidence of 45o, the refraction angle in two transparent media P and Q is 20o and 30o respectively. Which of the two is optically denser and why?

(b) Define 1 dioptre power of a lens

(c) Find the focal length denser and why?

23. How will you use two identical glass prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light ? Draw and label the ray diagram.

24. A person may suffer from both myopia and hypermetropia defects.
(a) What is this condition called?
(b) When does it happen?
(c) Name the type of lens often required by the persons suffering from this defect.
Draw labelled diagrams of such lenses.

#### SECTION – C [6 × 5 = 30 MARKS]

25. Define an alloy. How is an alloy prepared? List two advantages of making alloys. Write the composition of stainless steel. Why is steel preferred over iron? List two reasons.

26. Draw a neat diagram showing fertilisation in a flower and label
(a) Pollen tube,
(b) Male germ cell and
(c) Female germ cell, on it.

Explain the process of fertilisation in a flower. What happens to the
(i) ovary and
(ii) ovule after fertilisation ?

(OR)

(a) What is puberty ?

(b) Describe in brief the functions of the following parts in the human male reproductive system :

(i) Testes (ii) Seminal vesicle (iii) Vas deferens (iv) Urethra

(c) Why are testes located outside the abdominal cavity ?

(d) State how sperms move towards the female germ cell.

27. Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of 10 Ω, 20 Ω and 30 Ω connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following :
(a) Current through each resistor
(b) Total current in the circuit
(c) Total effective resistance of the circuit

(OR)

Two identical resistors, each of resistance 15 Ω, are connected in (i) series, and (ii) parallel, in turn to a battery of 6 V. Calculate the ratio of the power consumed in the combination of resistors in each case.

28. A cloth strip dipped in onion juice is used for testing a liquid “x”. The liquid “x” changes its colour. Which type of an indicator is onion juice.

The juice “x” turns blue litmus red. List observations the liquid “x” will show on reacting with the following.
a) Zinc granules
b) Solid sodium carbonate

Write the chemical equations for the reactions involved.

(OR)

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

29. (a) Why is nutrition necessary for the human body?

(b) What causes movement of food inside the alimentary canal?

(c) Why is the small intestine in herbivores longer than in carnivores?

(d) What will happen if mucus is not secreted by the gastric glands?

30. (a) State with reasons the mode of connecting all electrical appliances in common domestic electric circuits.

(b) Which two separate circuits are often used in domestic electric circuits and why?

(c) When does an electric short circuit occur? How can it be prevented?

## CBSE Class 10 Science Question Paper 2020 Set 3

Students can have a look at the CBSE Class 10 Science Question Paper 2020 Set 2 below:

### Science Set 3 Question Paper 2020

General Instructions:

I. This question paper comprises four sections – A, B and C. There are 30 questions in the question paper. All questions are compulsory.

II. Section A: Question numbers 1 to 14 – all questions or part thereof are of one marl each.These questions comprise multiple choice questions(MCQ), Very Short answer(VSA)and Assertion-Reason type question.Answer to these questions should be given in one word or one sentence.

III. Section B: Question numbers 15 to 24 are short answer type questions, carrying 3 marks each. Answers to these questions should not exceed 50 to 60 words.

IV. Section C: Question numbers 25 to 30 are long answer type questions, carrying 5 marks each.Answer to these questions should not exceed 80 to 90 words

V. Answers 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.

#### SECTION – A [10 × 1 = 10 MARKS]

1. Draw the structure of a carboxylic acid containing three carbon atoms.

2. When is the potential difference between two points in a current carrying conductor said to be 1 volt?

3. Answer question numbers 3(a) – 3(d) on the basis of your understanding of the following paragraph and the related concepts.

Around the year 1800, only 30 elements were known Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Mendeleev for classifying elements goes to Mendeleev for his most important contribution to the early development of a periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The format of their hydrides and oxides were treated as basic criteria for the classification of the elements. However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.

3(a). State Mendeleev’s periodic law.

3(b). Why did Mendeleev leave some gaps in the periodic table?

3(c). If the letter ‘R’ was used to represent and of the elements in the group, then the hydride and oxide of carbon would respectively be represented as

(i) $RH_{4}$, RO

(ii) $RH_{4}$, $RO_{2}$

(iii) $RH_{2}$, $RO_{2}$

(iv) $RH_{2}$, RO

3(d). Isotopes are

(i) Atoms of elements with similar chemical properties but different atomic masses.

(ii) Atoms of different elements with similar chemical properties but different atomic masses.

(iii) Atoms of elements with different chemical properties but same atomic masses.

(iv) Atoms of different elements with different chemical properties but same atomic masses.

4. Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts:

India today is facing the problem of overuse of resources, contamination of water and soil and luck of methods of processing the waste. The time has come for the world to say goodbye to “single-use plastics”. Steps must be undertaken to develop environment -friendly substitutes, effective plastic waste collection and methods of its disposal.

Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques. Bioremediation involves introducing microbes into a landfill to naturally ‘break’ it down and biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component. The city managed to chip away 15 lakh metric tonnes of waste at a cost of around Rs 10 crore. A similar experiment was successfully carried out in Ahmedabad also.

4(a). State two methods of effective plastic waste collection in your school.

4(b). Name any two uses of “single-use plastic” in daily life.

4(c). If we discontinue the use of plastic, how can an environment-friendly substitute be provided?

4(d). Do you think microbes will work similarly in landfill sites as they work in the laboratory? Justify your answer.

5. Choose the incorrect statement from the following :

I. Ozone is a molecule formed by three atoms of oxygen

II. Ozone shields the surface of the Earth from ultraviolet radiations

IV. Ozone gets decomposed by UV radiations

6. Food web is constituted by

I. Relationship between the organisms and the environment.

II. Relationship between plants and animals.

III. Various interlinked food chains in an ecosystem.

IV. Relationship between animals and environment.

7. Which of the following statements is not true about a ‘bud’ in ‘Hydra’?

I. It is an outgrowth.

II. It forms due to repeated cell division at one specific site.

III. It detaches from the parent body as soon as it is produced.

IV. It becomes a new independent individual.

8. Anaerobic process

I. Takes place in yeast during fermentation

II. Takes place in the presence of oxygen

III. Produces only energy in the muscles of human beings.

IV. Produces ethanol, oxygen and energy.

(OR)

Most of the digestion and absorption of the food takes place in the

I. Small intestine

II. Liver

III. Stomach

IV. Large intestine

9. Which of the following does not represent electrical power?

a) I2R

b) IR2

c) VI

d) V2/R

10. Which one of the following statements is not true about nuclear energy generation in a nuclear reactor?

(a) Energy is obtained by a process called nuclear fission.

(b) The nucleus of Uranium is bombarded with high energy neutrons.

(c) A chain reaction is set in the process.

(d) In this process a tremendous amount of energy is released at a controlled rate.

(OR)

The biggest source of energy on Earth’s surface is

I. Biomass

III. Tides

IV. Winds

11. Which one of the following statements is correct about the human circulatory system?

I. Blood transports only oxygen and not carbon dioxide

II. Human heart has five chambers

III. Valves ensure that the blood does not flow backwards

IV. Both oxygen-rich and oxygen-deficient blood gets mixed in the heart

12. If a person has five resistors each of value 1/5 Ω, then the maximum resistance he can obtain by connecting them is

(a) 1 Ω

b) 5 Ω

c) 10 Ω

d) 25 Ω

(OR)

The resistance of a resistor is reduced to half of its initial value. In doing so, if other parameters of the circuit remain unchanged, the heating effects in the resistor will become

I. Two times

II. Half

III. One-fourth

IV. Four times

For question numbers 13 and 14, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(1) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

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

(3) (A) is true, but (R) is false. (d) (A) is false, but (R) is true

13. Assertion (A): The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father.

Reason (R): A child who inherits X’ chromosome from his father would be a girl (XX), while a child who inherits a Y’ chromosome from the father would be a boy (XY).

14. Assertion (A): Following is a balanced chemical equation for the action of steam iron:

$3Fe + 4H_{2}O\rightarrow Fe_{3}O_{4} + 4H_{2}$

Reason (R): The law of conservation of mass holds good for a chemical equation.

#### SECTION – B [10 × 3 = 30 MARKS]

15. Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.

16. A cheetah, on seeing a prey, moves towards him at a very high speed. What causes the movement of his muscles? How does the chemistry of cellular components of muscles change during this event?

17. (a) How is a soap different from a detergent in composition?

(b) Design an activity to show that a detergent works well with all types of water while a soap does not.

18. Lead Nitrate solution is added to a test tube containing potassium iodide solution.

(a) Write the name and colour of the compound precipitated.

(b) Write the balanced chemical equation for the reaction involved.

(OR)

What happens when food materials containing fats and oils are left for a long time?

List two observable changes and suggest three ways by which this phenomenon can be prevented.

19. List three differentiating features between the process of galvanization and alloying.

(OR)

Compare in tabular form the reactivity of the following metals with cold and hot water.

a) Sodium

b) Calcium

c) Magnesium

20. Define the term variation. Why is variation beneficial to a species? List two reasons for the appearance among the progeny formed by sexual reproduction.

(OR)

List two distinguishing features between inherited and acquired characters. Also give one example for each type.

21. How will you use two identical glass prisms so that a narrow beam of white light incident on one emerges out of the second prism as white light? Draw and label the ray diagram.

22. A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm?

(a) Position of the image

(b) Size of the image

(c) Nature of the image Draw a labelled ray diagram to justify your inferences.

23. Which defect of the eye is known as far-sightedness? When does this defect arise? State two reasons. How is this defect corrected?

24. The refractive index of a medium x’ with respect to a medium y’ is 2/3 and the refractive index of medium y’ with respect to medium z’ is 4/3. Find the refractive index of medium z’ with respect to medium x’. If the speed of light in medium x’ is 3 x 108 ms-1, calculate the speed of light in medium ‘y’.

#### SECTION – C [6 × 5 = 30 MARKS]

25. A cloth strip dipped in onion juice is used for testing a liquid “x”. The liquid “x” changes its colour. Which type of an indicator is onion juice.

The juice “x” turns blue litmus red. List observations the liquid “x” will show on reacting with the following.

a) Zinc granules

b) Solid sodium carbonate

Write the chemical equations for the reactions involved.

(OR)

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

26. (a) Define the terms ‘alloy’ and ‘amalgam’. Name the alloy used for welding electric wires together and write its constituents.

(b) Name the constituents of the following alloys:

(i) Brass

(ii) Stainless steel

(iii) Bronze

State one property in each of these alloys which is different from its constituents.

27. (a) State Fleming’s Left-hand rule.

(b) List three characteristic features of the electric current used in our homes

(c) What is a fuse? Why is it called a safety device?

(d) Why is it necessary to earth metallic electric appliances?

28. (a) List the sequence of events in the uterus of a human female from fertilization of egg till childbirth

(b) State the changes that are observed in the uterus if fertilization of egg does not occur

29. (a) Why is nutrition necessary for the human body?

(b) What causes movement of food inside the alimentary canal?

(c) Why is the small intestine in herbivores longer than in carnivores?

(d) What will happen if mucus is not secreted by the gastric glands?

30. Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of 10 Ω, 20 Ω and 30 Ω connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following :

(a) Current through each resistor

(b) Total current in the circuit

(c) Total effective resistance of the circuit

(OR)

Two identical resistors, each of resistance 15 Ω, are connected in (i) series, and (ii) parallel, in turn to a battery of 6 V. Calculate the ratio of the power consumed in the combination of resistors in each case.

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