31/4/2 2020 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Which oils should be chosen for cooking to remain healthy ?
Ans: Oils containing unsaturated fatty acids/name of any edible oil.
2) Define the term induced electric current.
Ans: The electric current generated /induced in a conductor by changing magnetic field around it.
3) Answer question numbers 3(a) – 3(d) on the basis of your understanding of the following paragraph and the related studied 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 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 formulae 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.
Ans: The properties of elements are the periodic functions of their atomic masses.
3(b) Why did Mendeleev leave some gaps in the Periodic table ?
Ans: To fill with undiscovered elements.
3(c) If the letter ‘R’ was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as
(i) RH4 , RO
(ii) RH4 , RO2
(iii) RH2 , RO2
(iv) RH2 , RO
Ans: (ii)/RH4, RO2
3(d) Isotopes are
(i) Atoms of an element with similar chemical properties but different atomic masses.
(ii) Atoms of different elements with similar chemical properties but different atomic masses.
(iii) Atoms of an element with different chemical properties but same atomic masses.
(iv) Atoms of different elements with different chemical properties but same atomic masses.
Ans: (i)/Atoms of an element with similar chemical properties but different 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 lack 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 ₹ 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.
Ans: Use of separate bins for plastic and paper ; separation of biodegradable and non biodegradable wasteor any other.
4(b) Name any two uses of ‘‘single-use plastic’’ in daily life.
Ans:
- Packaging of articles like water, food, milk, biscuits etc.
- Disposable utility items –bowls, tumblers, plates , leaves etc.
4(c) If we discontinue the use of plastic, how can an environment-friendly substitute be provided ?
Ans: By providing cloth /jute /earthern pots and utensils/ paper or any other material for the similar purposes.
4(d) Do you think microbes will work similarly in landfill sites as they work in the laboratory ? Justify your answer.
Ans:
- Yes
- The action of microbes is tested in the laboratory creating the same conditions as in the landfill.
5) Fertilisation is the process of
(A) transfer of male gamete to female gamete.
(B) fusion of nuclei of male and female gamete.
(C) adhesion of male and female reproductive organs.
(D) the formation of gametes by a reproductive organ.
Ans: (B) /fusion of nuclei of male and female gamete.
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
(D) Urinary bladder
Ans: (B) / Nephron
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.
Ans: (B) / False feet developed in some unicellular organisms.
7) Which one of the following statements is correct about the human circulatory system ?
(A) Blood transports only oxygen and not carbon dioxide.
(B) Human heart has five chambers.
(C) Valves ensure that the blood does not flow backwards.
(D) Both oxygen-rich and oxygen-deficient blood gets mixed in the heart.
Ans: (C) / Valves ensure that the blood does not flow backwards.
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.
Ans: (B) / The nucleus of Uranium is bombarded with high energy neutrons.
OR
The biggest source of energy on Earth’s surface is
(A) Biomass
(B) Solar radiations
(C) Tides
(D) Winds
Ans: Biomass
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
Ans: (A) 1 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.
Ans: (B) /half
10) 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.
Ans: (B)/ The nucleus of Uranium is bombarded with high energy neutrons.
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%
Ans: (B) 10 %
12) Choose the incorrect statement from the following :
(A) Ozone is a molecule formed by three atoms of oxygen.
(B) Ozone shields the surface of the Earth from ultraviolet radiations.
(C) Ozone is deadly poisonous.
(D) Ozone gets decomposed by UV radiations.
Ans: Treat all answers as correct.
13) Assertion (A) : The reaction
MnO2 + 4HCl -> MnCl2 + 2H2O + Cl2
is an example of a redox reaction.
Reason (R) : In this reaction, HCl is reduced to Cl2 whereas MnO2 is oxidised to MnCl2
Ans: (c) / (A) is true, but ( R ) is false.
14) Assertion (A) : Wing 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 same function in different species are called analogous organs.
Ans: (a) / Both ( A ) and ( R) are true and ( R) is the correct explanation of assertion ( A).
SECTION B
15) When hydrogen sulphide gas is passed through a blue solution of copper sulphate, the colour of the solution fades and a black precipitate is obtained.
(a) Name the type of reaction mentioned above.
Ans: Double displacement reaction.
(b) Why does the colour of the solution fade away ?
Ans: Due to the formation of colourless sulphuric acid in the solution.
(c) Write the chemical name of the black precipitate formed.
Ans: Copper Sulphide / CuS
(d) Give the balanced chemical equation for the reaction involved.
Ans: CuSO4 + H2S -> CuS + H2SO4
OR
Study the figure given below and answer the following questions :
(a) Name the process depicted in the diagram.
Ans: Electrolysis of water
(b) Write the composition of the anode and the cathode.
Ans: Carbon electrodes / Graphite rod
(c) Write the balanced chemical equation of the reaction taking place in this case.
Ans:
(d) The reaction does not take place if a few drops of dilute sulphuric acid are not added to water. Why ?
Ans: Pure water is a non conductor of electricity /electric current is carried through the acidic solution by ions.
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
Ans: Behind the mirror.
(b) Size of the image
Ans: Magnified.
(c) Nature of the image Draw a labelled ray diagram to justify your inferences.
Ans: Virtual and erect.
17) Define the term evolution. ‘‘Evolution cannot be equated with progress.’’ Justify this statement.
Ans:
- Evolution – Gradual change in living organisms with time since the beginning of life resulting in the formation of a new species/ Evolution is simply the generation of diversity and the shaping of diversity by environmental selection.
- Evolution cannot be equated with progress because more and more complex body designs have emerged and evolved over time but this does not mean that older designs are inefficient.Foreg. Bacteria are simpler organisms but some inhabit the most inhospitable habitats like hot springs, deep sea, thermal vents and the ice in Antartica.
OR
‘‘During the course of evolution, organs or features may be adapted for new functions.’’ Explain this fact by choosing an appropriate example.
Ans: Examples of feathers :
– Feathers can start out as providing insulation in cold weather but later they might become useful for flight.
– Some dinosaurs have feathers but they could not fly.
– Birds later adapted the feathers for flight .
– This shows that birds are closely related to reptiles.
18) Write in tabular form the location and function of the hormones secreted by each of the following glands present in the human body :
(a) Pituitary gland
(b) Thyroid gland
(c) Pancreas
Ans:
Glands |
Location | Function |
a) Pituitary gland | Brain |
Stimulates growth in all organs. |
b) Thyroid |
Neck/ Larynx | Regulates metabolism of fats, proteins & carbohydrates. |
c) Pancreas | Below Stomach |
Regulates blood sugar |
19) List three differentiating features between the processes of galvanisation and alloying.
Ans:
Galvanisation |
Alloying |
1.) Coating a layer of zinc metal on the metal. |
1.) Mixing of a metal with metal or non-metal. |
2.) Not a homogeneous mixture. |
2.) Homogeneous mixture. |
3.) No change in physical properties of metals takes place. |
3.)Change in physical properties of metals takes place. |
4.) The process is an outcome of the reactivity of metals. |
4.) Reactivity of metals do not play any role in it. |
5.) Prevents rusting only. |
5.) Some alloys may prevent rusting and also used for other advantages. |
OR
Compare in tabular form the reactivities of the following metals with cold and hot water :
(a) Sodium
(b) Calcium
(c) Magnesium
Ans:
Cold Water |
Hot Water |
|
Sodium |
Reacts violently
Heat is evolved. |
React more violently More heat is evolved. |
Calcium |
Reacts less violently as compared to sodium. |
Reacts violently with hot water and sticks to surface of metal and floats on surface of water. |
Magnesium |
Does not react with cold water |
React with hot water and floats on surface of water. |
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.
Ans:
- Carbon atom, the first member of group 14 has the smallest size in the group and highest inter-atomic force of attraction.
- It has four valence electrons and requires four more electrons to attain stable configuration.
- Due to its small size, nucleus of carbon is able to hold the shared pairs of electrons strongly.
- The bonds formed by other elements of the same group are weaker due to bigger size of their atoms.
21) Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.
Ans: The movement of the growth of the roots downwards and the shoots upwards under the stimuli of gravity is called geotropism./ The movement of the part of the plant towards or away from the stimulus gravity.
22) (a) For the same angle of incidence of 45°, the refraction angle in two transparent media P and Q is 20 ° and 30 ° respectively. Which of the two is optically denser and why ?
Ans: (a) Medium P is optically denser than Q because in it the ray is bending more towards the normal as ∠p < ∠q
(b) Define 1 dioptre power of a lens.
Ans: 1 dioptre is the power of a lens whose focal length is 1 metre.
(c) Find the focal length of a lens of power + 0.5 D.
Ans: ) f (m) = 1 /P(D)
= 1/ +0.5D
= + 2m
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.
Ans: By placing second (identical) prism in an inverted position with respect to the first prism.
24) A person may suffer from both myopia and hypermetropia defects.
(a) What is this condition called ?
Ans: Presbyopia
(b) When does it happen ?
Ans: Gradual weakening of the ciliary muscles of the eye/ diminishing flexibility of the eye lens.
(c) Name the type of lens often required by the persons suffering from this defect. Draw labelled diagram of such lenses.
Ans: Bifocal lens
SECTION C
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.
Ans:
- Homogeneous mixture of two or more metals, or a metal and a non-metal.
- By first melting the primary metal,and then, dissolving the otherelements in it in definite proportions. It is then cooled at room temperature.
- Stainless steel- Iron, Nickel, Chromium
- Hard, does not rust.
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 ?
Ans:
- Process of fertilization : Pollen tube is formed from the pollen grain. Fusion of male germ cell with female germ cell to form zygote.
- Ovary- Changes into fruit
- Ovule- Changes into Seed
OR
(a) What is puberty ?
Ans: The period during adolescence is called puberty/age of males and females at which reproductive organs become functional.
(b) Describe in brief the functions of the following parts in the human male reproductive system :
(i) Testes
Ans: Testes – Production of sperms /Secretion of male sex hormone testosterone.
(ii) Seminal vesicle
Ans: Seminal vesicle – secretes a fluid which makes the transport of sperms easier/ the fluid secreted gives nutrition to sperms.
(iii) Vas deferens
Ans: Vas deferens- carries the sperms to the seminal vesicle.
(iv) Urethra
Ans: Urethra- forms a common passage for both the sperms and urine.
(c) Why are testes located outside the abdominal cavity ?
Ans: Because the sperm formation requires a lower temperature than the normal body temperature.
(d) State how sperms move towards the female germ cell.
Ans: With the help of a long tail.
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 :
Ans:
(a) Current through each resistor
Ans: 11=v/R1=6/10=0.6A
12=V/R2=6/20=0.3A
13=V/R3=6/30=0.2A
(b) Total current in the circuit
Ans: I= I1 + I2 + I3 = 1.1 A
(c) Total effective resistance of the circuit
Ans: Reff = V/ I
= 6 /1.1 = 5.4Ω
OR
Two identical resistors, each of resistance 15Ω, are connected in
Ans: R1 = R2 = 15Ω V= 6V
(i) series,
Ans: In series :
Rs = R1 + R2 = 15Ω + 15Ω = 30Ω
I = V R3 = 6V /30Ω = 0.2 A
∴ P1 = VI = 6V × 0.2 A = 1.2 W
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.
Ans: In parallel
Rp = R1 × R2 /R1 + R2 = 15 × 15/ 15 + 15 = 225/ 30 = 7.5Ω
I = V Rp = 6V /7.5Ω = 0.8 A
P2 = VI = 6V × 0.8 A = 4.8W
Ratio of power = P1/ P2 = 1.2W/ 4.8W = 1 /4
∴ P1 ∶ P2 = 1 ∶4
28) A cloth strip dipped in onion juice is used for testing a liquid ‘X’. The liquid ‘X’ changes its odour. Which type of an indicator is onion juice ? The liquid ‘X’ turns blue litmus red. List the observations the liquid ‘X’ will show on reacting with the following :
(a) Zinc granules
Ans: Colourless and Odourless gas is evolved with bubbles .
Zinc + Acid -> Zinc Salt + H2 ↑
(b) Solid sodium carbonate Write the chemical equations for the reactions involved.
Ans: Brisk effervescence/ colourless and odourless gas is evolved.
Sodium carbonate + Acid ->Sodium salt of Acid + Water + Carbon dioxide↑
( or by using any example of acid like HCl/ H2SO4)
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 ?
Ans:
- Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
- Examples CuSO4 .5H2O
Na2CO3.10 H2O
- Heat a few crystals of hydrated copper sulphate( bluecolour) in a dry boiling tube. Water droplets are seen in the boiling tube.
Colour : The colour of copper sulphate changes to white .
State : The blue crystal changes to white powder.
29) (a) Why is nutrition necessary for the human body ?
Ans: For providing energy for various metabolic processes / Formation of new cells / Repair of damaged or worn out cells & tissues / Developing resistance against diseases.
(b) What causes movement of food inside the alimentary canal ?
Ans: Peristaltic movement / Peristalsis/ Rhythmic contraction and relaxation of the muscles in the lining of alimentary canal.
(c) Why is small intestine in herbivores longer than in carnivores ?
Ans: Herbivores eat plant matter which is rich in cellulose and takes longer time to digest and hence longer small intestine.
(d) What will happen if mucus is not secreted by the gastric glands ?
Ans: The inner lining of the stomach will not be protected from the action of the acid /HCl
30) (a) State with reasons the mode of connecting all electrical appliances in common domestic electric circuits.
Ans: Mode : Parallel arrangement Reasons :
- Voltage across each appliance is same.
- Selective operation of devics is possible /separate switch can be provided in the circuit for each appliance.
- If one device is defective or non-operational, working of others is not affected.
(b) Which two separate circuits are often used in domestic electric circuits and why ?
Ans: 5 A
15 A
Due to difference in power rating of appliances used in household.
(c) When does an electric short circuit occur ? How can it be prevented ?
Ans: When live wire and neutral wire come in direct contact/ overloading.
Prevention :
By the use of fuse/ using good quality cables.
CBSE Class 10 Previous Question Paper 2020 Solution
- Science (Set No 31/1/1)
- Science (Set No 31/1/2)
- Science (Set No 31/1/3)
- Science (Set No 31/2/1)
- Science (Set No 31/2/2)
- Science (Set No 31/2/3)
- Science (Set No 31/3/1)
- Science (Set No 31/3/2)
- Science (Set No 31/3/3)
- Science (Set No 31/4/1)
- Science (Set No 31/4/2)
- Science (Set No 31/4/3)
- Science (Set No 31/5/1)
- Science (Set No 31/5/2)
- Science (Set No 31/5/3)