31/ 3/ 2 2020 Class 10 Science Question Paper Solution
Section – A
(1) Define electropositivity.
Ans: Tendency of an element to lose electrons.
OR
The atomic radii of first group elements are given below :
Group-I element | Atomic Radii (pm) |
Na | 86 |
K | 231 |
Rb | 244 |
Cs | 282 |
State the reason behind the observed trend in the above elements.
Ans: Atomic radii increases from Na to Cs due to addition of new shells.
(2) How are covalent bonds formed?
Ans: Covalent bonds are formed by sharing of electron pair /pairs between two atoms.
(3) Questions numbers 3(a) to 3(d) are based on table given below. Study the table in which the levels of Thyroid Stimulating Hormone (TSH) in women are given and answer the questions that follow on the basis of understanding of the following paragraph and the related studied concepts.
Age Range | Normal (mU/L) | Low (mU/L) |
18 – 29 years | 0.4 – 2.34 mU/L | < 0.4 mU/L |
30 – 49 years | 0.4 – 4.0 mU/L | < 0.4 mU/L |
50 – 79 years | 0.46 – 4.68 mU/L | < 0.46 mU/L |
Women are at greater risk for developing abnormal TSH levels during menstruation, while giving birth and after going through menopause. Around 5% of women in the United States have some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 study showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules.
(a) A 35 year old woman has TSH level 6.03 mU/L. What change should she bring in her diet to control this level?
Ans: She should monitor iodine intake in her diet.
(b) When do women face a greater risk of abnormal TSH level?
Ans: During menstruation / during pregnancy and after going through menopause.
(c) State the consequence of low TSH level.
Ans: Low TSH level leads to swelling of neck region / disease called goiter.
(d) Name the mineral that is responsible for synthesis of hormone secreted by thyroid gland.
Ans: Iodine
(4) Answer question numbers 4(a) to 4(d) on the basis of your understanding of the following paragraph and the related studies concepts.
The Tehri dam is the highest dam in India and one of the highest in the World. The Tehri dam withholds a reservoir of capacity 4.0 km3 and surface area 52 km2 . It is used for irrigation, municipal water supply and the generation of 1000 MW of hydro electricity.
The Tehri Dam has been the object of protests. Environment activist Shri Sunder Lal Bahuguna led the “Anti Tehri Dam Movement” from 1980s to 2014. The protest was against the displacement of town inhabitants and environmental consequences of the weak ecosystem. The relocation of more than 1,00,000 people from the area has led to protracted legal battles over resettlement rights and ultimately resulted in the delayed completion of the project.
(a) How is hydropower harnessed?
Ans: Hydropower is harnessed by converting the potential energy of falling water from a height into electricity.
(b) Define 1 MW.
Ans: It is the power developed when 106 J of work is done per second. / 1MW = 106 watts.
(c) Mention two disadvantages of constructing Tehri Dam.
Ans: Loss of agricultural land / displacement of a large number of peasants and tribals/ destruction of ecosystem.
(d) What happens when water from great heights is made to fall on blades of turbine?
Ans: The blades of turbine move the armature of a generator with high speed to generate electricity.
(5) An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be
(a) Group 1 and Period 3
(b) Group 2 and Period 3
(c) Group 13 and Period 3
(d) Group 16 and Period 3
Ans: Group 16 and Period 3
OR
Consider the following statements about an element ‘X’ with number of protons 13.
(A) It forms amphoteric oxide
(B) Its valency is three
(C) The formula of its chloride is XCl3
The correct statements(s) is/are
(a) only (A)
(b) only (B)
(c) (A) and (C)
(d) (A), (B) and (C)
Ans: (d) / (A), (B) & (C)
(6) An aqueous solution ‘A’ turns phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, the pink colour disappears. The following statement is true for solution ‘A’ and ‘B’.
(a) A is strongly basic and B is a weak base.
(b) A is strongly acidic and B is a weak acid.
(c) A has pH greater than 7 and B has pH less than 7.
(d) A has pH less than 7 and B has pH greater than 7.
Ans: A has pH greater than 7 and B has pH less than 7.
(7) In which of the following, the identity of initial substance remains unchanged ?
(a) Curdling of milk
(b) Formation of crystals by process of crystallisation
(c) Fermentation of grapes
(d) Digestion of food
Ans: Formation of crystals by process of crystallisation.
(8) Several factories were pouring their wastes in rivers A and B. Water samples were collected from these two rivers. It was observed that sample collected from river A was acidic while that of river B was basic. The factories located near A and B are
(a) Soaps and detergents factories near A and alcohol distillery near B.
(b) Soaps and detergents factories near B and alcohol distillery near A.
(c) Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
(d) Lead storage battery manufacturing factories near B and soaps and detergents factories near A.
Ans: Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
(9) A diagram of traditional water harvesting system is given below : The statement which defines the system and its parts is
(a) This is an ideal setting of the Khadin system and A = Catchment area; B = Saline area & C = Shallow dugwell
(b) This is an ideal setting of the Shallow dugwell system and A = Catchment area; B = Saline area and C = Khadin
(c) This is an ideal setting of Catchement area and A = Khadin, B = Saline area and C = Shallow dugwell
(d) This is showing Saline area and A = Catchment area; B = Khadin and C = Shallow dugwell
Ans: This is an ideal setting of the Khadin system and A= catchment area; B= Saline area ; C=Shallow dugwell.
OR
The major ill effect of mono culture practice in forests is on the
(a) biodiversity which faces large destruction
(b) local people whose basic needs can no longer be met from such forests
(c) industries
(d) forest department
Ans: biodiversity which faces large destruction.
(10) The maximum resistance which can be made using four resistors each of resistance 1/2 W is
(a) 2 W
(b) 1 W
(c) 2.5 W
(d) 8 W
Ans: 2 W
(11) A cylindrical conductor of length ‘l’ and uniform area of cross section ‘A’ has resistance ‘R’. The area of cross section of another conductor of same material and same resistance but of length ‘2l’ is
(a) A/2
(b) 3A/ 2
(c) 2A
(d) 3A
Ans: 2A
(12) The sky appears dark to passengers flying at very high altitudes mainly because:
(a) Scattering of light is not enough at such heights.
(b) There is no atmosphere at great heights.
(c) The size of molecules is smaller than the wavelength of visible light.
(d) The light gets scattered towards the earth.
Ans: Scattering of light is not enough at such heights
Note : For question numbers 13 and 14, two statements are given-one labelled 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.
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
(13) Assertion (A) : Alloys are commonly used in electrical heating devices like electric iron and heater.
Reason (R) : Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points then their constituent metals.
Ans: A is true but R is false.
(14) Assertion (A): Following are the members of a homologous series : CH3OH, CH3CH2OH, CH3CH2CH2OH
Reason (R) : A series of compounds with same functional group but differing by – CH2 – unit is called a homologous series.
Ans: Both (A) and (R) are true and (R) is the correct explanation of the assertion.
Section – B
(15) Complete and balance the following chemical equations:
(i) Na OH(aq) + Zn(s) →
Ans: 2NaOH (aq) + Zn (s) → Na2 Zn O2(aq) + H2(g)
(ii) CaCO3(s) + H2O (l)+ CO2(g) →
Ans: CaCO3(s)+H2O(l) + CO2(g) → Ca (HC03)2(aq)
(iii) HCL(aq) + H2O(l) →
Ans: HCl (aq) + H2O(l) → H3O + (aq) + Cl– (aq)
OR
During electrolysis of brine, a gas ‘G’ is liberated at anode. When this gas ‘G’ is passed through slaked lime, a compound ‘C’ is formed, which is used for disinfecting drinking water.
(i) Write formula of ‘G’ and ‘C’.
Ans: G = Cl2
C = CaOCl2
(ii) State the chemical equation involved.
Ans: Ca(OH)2 + Cl2 → Ca OCl2 + H2O
(iii) What is common name of compound ‘C’? Give its chemical name.
Ans: Common name – Bleaching Powder
Chemical name – Calcium Oxychloride
(16) Mention with reason the colour changes observed when :
(i) silver chloride is exposed to sunlight.
Ans: White to grey
Reason : Silver chloride decomposes to produce silver and chlorine.
(ii) copper powder is strongly heated in the presence of oxygen.
Ans: Brown to black
Reason : Copper oxide is produced on heating.
(iii) a piece of zinc is dropped in copper sulphate solution.
Ans: Blue to colourless
Reason : Zinc Sulphate is formed.
(17) Three elements X, Y and Z have atomic numbers 7, 8 and 9 respectively.
(a) Arrange them in the decreasing order of their atomic radii.
Ans: X > Y > Z
(b) Which of the three is most electronegative? Why?
Ans: Z; needs only one electron to attain stable configuration
(c) Write the formula of compound formed between (i) X and Y (ii) X and Z
Ans: (i) X2Y3
(ii) XZ3
(18) (a) State the role played by the following in the process of digestion.
(i) Enzyme trypsin
Ans: (i) Enzyme trypsin : Helps in the digestion of proteins.
(ii) Enzyme lipase
Ans: (ii) Enzyme lipase : Helps in the breaking down of emulsified fats.
(b) List two functions of finger like projections present in the small intestine.
Ans: Two functions :
- Increase the surface area,
- Helps in absorption of digested food.
(19) (a) Define ecosystem.
Ans: Ecosystem : It is the interaction between living / biotic and non- living / abiotic components in an area / environment.
(b) Autotrophs are at the first level of food chain. Give reason.
Ans: Because autotrophs have the ability to trap solar energy and convert it into food by photosynthesis and transfer food energy to the next level in a food chain.
(c) In a food chain of frogs, grass, insects and snakes assign trophic level to frogs. To which category of consumers do they belong to?
Ans: Frogs : Third Trophic level ; Secondary consumers
OR
(a) Explain the role of UV radiation in producing ozone layer.
Ans: High energy UV radiations split apart some molecular oxygen into free (O) atoms, these atoms combine with molecular oxygen to form ozone.
(b) Mention the reaction involved.
Ans:
(c) Why is excessive use of CFCs a cause of concern?
Ans:
- Depletion of the ozone layer.
- If these UV radiations reach the earth they may cause skin cancer in human beings.
(20) List three factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species and why?
Ans: Three factors :-
- Natural Selection
- Genetic Drift
- Geographical Isolation
- Mutations
- Geographical Isolation
- because pollination is ocurring in the same plant which does not bring much variations leading to no evolution .
(21) A green stemmed rose plant denoted by GG and a brown stemmed rose plant denoted by gg are allowed to undergo a cross with each other.
(a) List your observations regarding
(i) Colour of stem in their F1 progeny
Ans: Green
(ii) Percentage of brown stemmed plants in F2 progeny if F1 plants are self pollinated.
Ans: 25 %
(iii) Ratio of GG and Gg in the F2 progeny
Ans: GG : Gg
1 : 2
(b) Based on the finding of this cross, what conclusion can be drawn?
Ans: The traits which are expressed in F1 progeny are called dominant traits, whereas the traits which are unable to express themselves in F1 progeny but reappear in the F2 progeny are called recessive traits.
(22) (a) Water has refractive index 1.33 and alcohol has refractive index 1.36. Which of the two medium is optically denser ? Give reason for your answer.
Ans: Alcohol is optically denser medium.
Reason : A medium having higher refractive index is an optically denser medium.
(b) Draw a ray diagram to show the path of a ray of light passing obliquely from water to alcohol.
(c) State the relationship between angle of incidence and angle of refraction in the above case.
Ans: Angle of incidence is greater than angle of refraction / sin i/ sin r = constant
(23) (a) With the help of labelled ray diagram show the path followed by a narrow beam of monochromatic light when it passes through a glass prism.
Ans:
(b) What would happen if this beam is replaced by a narrow beam of white light?
Ans:
(b) Splitting into seven colours / Dispersion / VIBGYOR /
OR
(a) A person is suffering from both myopia and hypermetropia.
(i) What kind of lenses can correct this defect?
Ans: (i) Bifocal Lens
(ii) How are these lenses prepared?
Ans: Upper part of lens is concave and lower part of the lens is convex. /
(b) A person needs a lens of power + 3D for correcting his near vision and –3D for correcting his distant vision. Calculate the focal lengths of the lenses required to correct these defects.
Ans: P = +3D
f = 1/ P
= 1/3 m = +100 /3 cm = + 33.3 cm
P = – 3D
f = −100 /3 = −33.3 cm
(24) Give reasons for the following:
(i) There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
Ans: The strength of magnetic field is higher near the poles /ends of solenoid.
(ii) The current carrying solenoid when suspended freely rests along a particular direction.
Ans: A current carrying solenoid behaves as a bar magnet.
(iii) The burnt out fuse should be replaced by another fuse of identical rating.
Ans: If a fuse , with a defined rating , is replaced by one with a larger rating then the fuse wire will not burn even when a current greater than safe limit is flowing. As a result the electrical circuit / appliances will be damaged.
Section – C
(25) Write balanced chemical equations to explain what happens, when
(i) Mercuric oxide is heated.
Ans: 2HgO 2 Hg + O2
(ii) Mixture of cuprous oxide and cuprous sulphide is heated.
Ans: 2Cu2 O + 2Cu2S 6Cu + SO2
(iii) Aluminium is reacted with manganese dioxide.
Ans: 3MnO2 + 4 Al → 2Al2O3 + 3Mn +heat
(iv) Ferric oxide is reduced with aluminium.
Ans: Fe2O3 + 2 Al → Al2O3 + 2Fe + heat
(v) Zinc carbonate undergoes calcination.
Ans: ZnCO3 ZnO + CO2
OR
(i) By the transfer of electrons, illustrate the formation of bond in magnesium chloride and identify the ions present in this compound.
(ii) Ionic compounds are solids. Give reasons.
Ans: In ionic compounds , very strong forces of attraction exist between positive and negative ions.
(iii) With the help of a labelled diagram show the experimental set up of action of steam on a metal.
(26) (a) Carry out following conversions:
(i) Ethanol to ethene
Ans: CH3CH2OH CH2 = CH2 + H2 O
(ii) Ethanol to Ethanoic acid
Ans: CH3CH2OH CH3COOH
(b) Differentiate between addition reaction and substitution reaction. Give one example of each.
Ans:
Addition Reaction | Substitution Reaction |
Unsaturated hydrocarbons add hydrogen in the presence of catalysts to give saturated hydrocarbons.
Example –
|
One type of atom or a group of atoms takes the place of another in a compound.
Example-
|
(27) (a) How do leaves of plants help in excretion? Explain briefly.
Ans:
- Oxygen and CO2 produced during photosynthesis and respiration is given out through stomata in the leaves.
- Excess water is given out by the process of transpiration.
- When leaves become old, they fall off carrying waste materials along with them in their vacuoles
(b) Describe the structure and function of a nephron.
Ans: Structure of Nephron :-
Nephron is the basic filtration unit in the kidney which is made of fine tubules, one end of which forms a cup-shaped structure called Bowman’s capsule, and the other end opens into a collecting duct/tube.
Function of Nephron :-
Blood carrying nitrogenous wastes is filtered through the glomerulus and is collected in the Bowman’s capsule, some useful substances in the filtrate like glucose and water etc are selectively reabsorbed as the filtrate flows along the tube
(28) (a) Draw a diagram showing germination of pollen on stigma of a flower and mark on it the following organs/parts :
(i) Pollen Grain
(ii) Pollen tube
(iii) Stigma
(iv) Female germ cell
(b) State the significance of pollen tube.
Ans: Pollen tube carries the male germ cell to reach the ovary and fuse with the female germ cell.
(c) Name the parts of flower that develop after fertilization into
(i) Seed
(ii) Fruit
Ans: (i) Seed ← Ovule
(ii) Fruit ← Ovary
OR
(a) “Use of a condom is beneficial for both the sexes involved in a sexual act.” Justify this statement giving two reasons.
Ans: Two reasons :
- Avoids unwanted/undesirable pregancies/ STD’s
- Use of condom prevents the transmission of infections from one person to another.
(b) How do oral contraceptive help in avoiding pregnancies?
Ans: Oral contraceptives change the hormonal balance of the body so that the eggs are not released.
(c) What is sex selective abortion ? How does it affect a healthy society ? (State any one consequence)
Ans: Sex selective abortion is a procedure that is done for female foetuses / female foeticide. It adversely affects the male-female sex ratio.
(29) (a) Define Power and state its SI unit.
Ans: Power is defined as rate of doing work/ rate at which energy is consumed/ rate at which electric energy is dissipated in an electric circuit.
S.I unit of Power is watt
(b) A torch bulb is rated 5 V and 500 mA. Calculate its
(i) Power
Ans: P = VI
= 5 volt × 500 mA
= 5 volt × 500 /1000 A
= 2.5 watt
(ii) Resistances
Ans: P = V 2 /R
or
R = 5 volt X 5 volt/ 2.5 watt
R = 250 /25 = 10 Ω
(iii) Energy consumed when it is lighted for 2½ hours.
Ans: Energy Consumed = Power × Time
= 2.5 W × 2.5h
= 6.25 Wh
(30) (a) A security mirror used in a big showroom has radius of curvature 5 m. If a customer is standing at a distance of 20 m from the cash counter, find the position, nature and size of the image formed in the security mirror.
Ans: It is a convex mirror.So focal length should be positive.
Radius of curvature R= + 5 m
∴ focal length f = 5 /2 = +2.5 m
Object distance u= -20m
Mirror formula 1/ v + 1/ u = 1/ f
1/ v + 1/ −20 = 1/ 2.5
1/ v = 1 /20 + 1/ 2.5
1/ v = 1 /20 + 10 /25
v = 5+ 40 /100 = 45/ 100
v = 100/ 45 = 20 /9 = +2.2m
- Nature of image = virtual and erect image
- Size of image : diminished image
(b) Neha visited a dentist in his clinic. She observed that the dentist was holding an instrument fitted with a mirror. State the nature of this mirror and reason for its use in the instrument used by dentist.
Ans: Concave Mirror Reason : to obtain erect and enlarged image of teeth
OR
Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose.
(i) State the nature of the lens and reason for its use.
Ans: Convex lens to get a magnified image of the lines on the palm.
(ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object?
Ans: Between F and 2F of the lens / or at F of the lens
(iii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.
Ans: focal length f = +10 cm
object distance u = -5 cm
Lens formula
v − 1 /u = 1/ f
1/v − 1 /−5 = 1/ 10
1 /v + 1 /5 = 1/ 10
1 /v = 1/ 10 − 1 /5 = 1−2/ 10
1/v = −1 /10
v = −10 cm
- m = himage /hobject = v/ u
= −10/ −5 = 2
Size of image is 2 times the size of object.
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)